From 63aa7b01c8b27d9c0079129585b48d4a38bc3489 Mon Sep 17 00:00:00 2001
From: Arun KV <65647132+arun-kv@users.noreply.github.com>
Date: Wed, 14 May 2025 09:24:36 +0530
Subject: [PATCH 01/13] SSV-24782:Create MSVC-specific wrapper library for
 reading CR8 register (#101)

* Create MSVC-specific wrapper library for reading CR8 register

Added a new C file that defines read_cr8_msvc(), which wraps the MSVC intrinsic __readcr8()
to read the CR8 register, since Clang and GCC do not provide __readcr8().

This function is now compiled into a separate library spl_cr_wrappers,
allowing Clang projects to call read_cr8_msvc() without directly depending
on MSVC-specific intrinsics in Clang code.
---
 module/os/windows/spl/CMakeLists.txt    | 36 ++++++++++++++++++++++++-
 module/os/windows/spl/spl-windows.c     |  2 +-
 module/os/windows/spl/spl_cr_wrappers.c | 21 +++++++++++++++
 module/os/windows/zfs/CMakeLists.txt    |  2 +-
 4 files changed, 58 insertions(+), 3 deletions(-)
 create mode 100644 module/os/windows/spl/spl_cr_wrappers.c

diff --git a/module/os/windows/spl/CMakeLists.txt b/module/os/windows/spl/CMakeLists.txt
index b63c54e57921..b1840072271d 100644
--- a/module/os/windows/spl/CMakeLists.txt
+++ b/module/os/windows/spl/CMakeLists.txt
@@ -40,6 +40,40 @@ wdk_add_library(splkern
   ${TMH_FILE_LIST}
 )
 
+target_include_directories(splkern BEFORE PUBLIC "${CMAKE_SOURCE_DIR}/include/os/windows/" PUBLIC "${CMAKE_SOURCE_DIR}/include/os/windows/spl")
 # set(CMAKE_TOOLCHAIN_FILE $ENV{CMAKE_TOOLCHAIN_FILE})
 
-target_include_directories(splkern BEFORE PUBLIC "${CMAKE_SOURCE_DIR}/include/os/windows/" PUBLIC "${CMAKE_SOURCE_DIR}/include/os/windows/spl")
+find_program(MSVC_CL_EXECUTABLE cl.exe)
+if(NOT MSVC_CL_EXECUTABLE)
+    message(FATAL_ERROR "MSVC_CL_EXECUTABLE is not set! Make sure to run CMake with a configured compiler.")
+else()
+    message(STATUS "MSVC_CL_EXECUTABLE is set to: ${MSVC_CL_EXECUTABLE}")
+endif()
+
+find_program(MSVC_LIB_EXECUTABLE lib.exe)
+if(NOT MSVC_LIB_EXECUTABLE)
+    message(FATAL_ERROR "MSVC lib.exe not found in PATH. Ensure you're using Visual Studio Command Prompt or MSVC toolchain.")
+else()
+message(STATUS "MSVC_LIB_EXECUTABLE is set to: ${MSVC_LIB_EXECUTABLE}")
+endif()
+
+set(CR_WRAPPERS_DIR "${CMAKE_BINARY_DIR}/module/os/windows/spl")
+file(MAKE_DIRECTORY "${CR_WRAPPERS_DIR}")
+
+set(CR_WRAPPERS_OBJ "${CR_WRAPPERS_DIR}/spl_cr_wrappers.obj")
+set(CR_WRAPPERS_LIB "${CR_WRAPPERS_DIR}/spl_cr_wrappers.lib")
+
+add_custom_command(
+    OUTPUT ${CR_WRAPPERS_LIB}
+    COMMAND ${MSVC_CL_EXECUTABLE} /nologo /c /Fo"${CR_WRAPPERS_OBJ}" ${CMAKE_SOURCE_DIR}/module/os/windows/spl/spl_cr_wrappers.c
+    COMMAND ${MSVC_LIB_EXECUTABLE} /nologo /OUT:${CR_WRAPPERS_LIB} /MACHINE:x64 ${CR_WRAPPERS_OBJ}
+    WORKING_DIRECTORY ${CR_WRAPPERS_DIR}
+    DEPENDS ${CMAKE_SOURCE_DIR}/module/os/windows/spl/spl_cr_wrappers.c
+    COMMENT "Building ${CR_WRAPPERS_LIB} in ${CR_WRAPPERS_DIR} using MSVC"
+)
+
+add_custom_target(cr_wrappers ALL DEPENDS ${CR_WRAPPERS_LIB})
+add_library(spl_cr_wrappers STATIC IMPORTED GLOBAL)
+set_target_properties(spl_cr_wrappers PROPERTIES
+    IMPORTED_LOCATION ${CR_WRAPPERS_LIB})
+
diff --git a/module/os/windows/spl/spl-windows.c b/module/os/windows/spl/spl-windows.c
index ae3135208fef..e6b31edac923 100644
--- a/module/os/windows/spl/spl-windows.c
+++ b/module/os/windows/spl/spl-windows.c
@@ -73,7 +73,7 @@ uint32_t spl_hostid = 0;
 uint64_t
 __readcr8(void)
 {
-	return (0ULL);
+	return (read_cr8_msvc());
 }
 
 unsigned long
diff --git a/module/os/windows/spl/spl_cr_wrappers.c b/module/os/windows/spl/spl_cr_wrappers.c
new file mode 100644
index 000000000000..529fe45df92c
--- /dev/null
+++ b/module/os/windows/spl/spl_cr_wrappers.c
@@ -0,0 +1,21 @@
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#include <stdint.h>
+
+// we can use the MSVC-specific intrinsic __readcr8() to read the value of the CR8
+// register directly. This intrinsic is part of MSVC's built-in functions,
+// which allows us to access hardware-level registers without writing assembly code.
+
+// Clang does not support the __readcr8 intrinsic, as it is specific to MSVC. 
+// Clang does not have a direct equivalent 
+// for accessing the CR8 register via a built-in function. Therefore, if we are using 
+// Clang, we must either use inline assembly or a different method to access the register.
+// https://learn.microsoft.com/en-us/cpp/intrinsics/readcr8?view=msvc-170
+
+__declspec(dllexport) uint64_t read_cr8_msvc(void) {
+    return __readcr8();
+}
+#else
+#error "_MSC_VER not defined"
+#endif
diff --git a/module/os/windows/zfs/CMakeLists.txt b/module/os/windows/zfs/CMakeLists.txt
index 4a778d957f8f..ce832e0bb43c 100644
--- a/module/os/windows/zfs/CMakeLists.txt
+++ b/module/os/windows/zfs/CMakeLists.txt
@@ -47,4 +47,4 @@ zvol_os.c
 ${TMH_FILE_LIST}
 )
 
-target_link_libraries(zfskern_os PRIVATE splkern icpkern)
+target_link_libraries(zfskern_os PRIVATE splkern icpkern spl_cr_wrappers)

From b461b51a10098b7784907cf28b5f707790fc09ca Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Tue, 6 Jan 2026 14:09:28 +0530
Subject: [PATCH 02/13] Added support to prealloc the abd cache Registry
 'zfs_abd_prealloc_percent' can be used to set the percent of prealloc wrt
 zfs_arc_max

---
 include/os/windows/zfs/sys/kstat_windows.h |  2 +
 module/os/windows/spl/spl-kmem.c           | 55 ++++++++++++++++++++++
 module/os/windows/zfs/arc_os.c             |  2 +
 module/os/windows/zfs/zfs_kstat_windows.c  |  7 ++-
 module/os/windows/zfs/zvol_os.c            |  1 +
 5 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/include/os/windows/zfs/sys/kstat_windows.h b/include/os/windows/zfs/sys/kstat_windows.h
index 644b01354177..3d1a510b9d06 100644
--- a/include/os/windows/zfs/sys/kstat_windows.h
+++ b/include/os/windows/zfs/sys/kstat_windows.h
@@ -150,6 +150,7 @@ typedef struct windows_kstat {
 	kstat_named_t zfs_removal_suspend_progress;
 	kstat_named_t cpu_avx_supported;
 	kstat_named_t zvol_io_threads;
+	kstat_named_t zfs_abd_prealloc_percent;
 } windows_kstat_t;
 
 
@@ -261,6 +262,7 @@ extern int zfs_autoimport_disable;
 extern int zfs_removal_suspend_progress;
 extern int cpu_avx_supported;
 extern int zvol_threads;
+extern int zfs_abd_prealloc_percent;
 
 int  kstat_windows_init(void *);
 void kstat_windows_fini(void);
diff --git a/module/os/windows/spl/spl-kmem.c b/module/os/windows/spl/spl-kmem.c
index 3a57b55ea90d..1ebd03d777c9 100644
--- a/module/os/windows/spl/spl-kmem.c
+++ b/module/os/windows/spl/spl-kmem.c
@@ -76,6 +76,7 @@ static volatile _Atomic int64_t spl_free = 0;
 int64_t spl_free_delta_ema;
 
 static boolean_t spl_event_thread_exit = FALSE;
+static boolean_t spl_abd_prealloc_thread_exit = FALSE;
 PKEVENT low_mem_event = NULL;
 
 static volatile _Atomic int64_t spl_free_manual_pressure = 0;
@@ -4914,6 +4915,56 @@ spl_event_thread(void *notused)
 	thread_exit();
 }
 
+extern kmem_cache_t *abd_chunk_cache;
+extern uint64_t zfs_arc_max;
+extern int zfs_abd_prealloc_percent;
+
+static void
+spl_abd_prealloc_thread(void *notused)
+{
+	NTSTATUS Status;
+
+	typedef struct abd_prealloc_node {
+		list_node_t node;
+	} abd_prealloc_node_t;
+
+	abd_prealloc_node_t *node;
+	list_t abd_prealloc_list;
+
+	KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "SPL: abd prealloc start segkmem_total_mem_allocated: %lld total_memory: %lld\n",
+	    segkmem_total_mem_allocated, total_memory));
+
+	dprintf("SPL: beginning spl_abd_prealloc_thread() loop\n");
+
+	list_create(&abd_prealloc_list, sizeof (abd_prealloc_node_t), offsetof(abd_prealloc_node_t, node));
+
+	while (!spl_abd_prealloc_thread_exit) {
+
+		if (!abd_chunk_cache || !zfs_arc_max) {
+			delay(hz);
+			continue;
+		}
+		node = (abd_prealloc_node_t *)kmem_cache_alloc(abd_chunk_cache, KM_SLEEP);
+		list_insert_tail(&abd_prealloc_list, node);
+
+		if (segkmem_total_mem_allocated >=
+                    (zfs_arc_max * zfs_abd_prealloc_percent) / 100) {
+                        break;
+                }
+	}
+
+	while ((node = list_remove_head(&abd_prealloc_list)) != NULL) {
+		kmem_cache_free(abd_chunk_cache, node);
+	}
+
+	spl_abd_prealloc_thread_exit = FALSE;
+	dprintf("SPL: %s thread_exit\n", __func__);
+
+	KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "SPL: abd prealloc done segkmem_total_mem_allocated: %lld total_memory: %lld zfs_prealloc_percent: %d%\n",
+	    segkmem_total_mem_allocated, total_memory, zfs_abd_prealloc_percent));
+	thread_exit();
+}
+
 
 static int
 spl_kstat_update(kstat_t *ksp, int rw)
@@ -5344,6 +5395,9 @@ spl_kmem_thread_init(void)
 
 	spl_event_thread_exit = FALSE;
 	(void) thread_create(NULL, 0, spl_event_thread, 0, 0, 0, 0, 92);
+
+	spl_abd_prealloc_thread_exit = FALSE;
+	(void) thread_create(NULL, 0, spl_abd_prealloc_thread, 0, 0, 0, 0, 92);
 }
 
 void
@@ -5351,6 +5405,7 @@ spl_kmem_thread_fini(void)
 {
 	shutting_down = 1;
 
+	spl_abd_prealloc_thread_exit = TRUE;
 	if (low_mem_event != NULL) {
 		dprintf("SPL: stopping spl_event_thread\n");
 		spl_event_thread_exit = TRUE;
diff --git a/module/os/windows/zfs/arc_os.c b/module/os/windows/zfs/arc_os.c
index 41eef66413f3..60cca3b399ed 100644
--- a/module/os/windows/zfs/arc_os.c
+++ b/module/os/windows/zfs/arc_os.c
@@ -696,6 +696,7 @@ arc_kstat_update_windows(kstat_t *ksp, int rw)
 		zfs_arc_average_blocksize =
 		    ks->arc_zfs_arc_average_blocksize.value.ui64;
 		zvol_threads = ks->zvol_io_threads.value.ui32;
+		zfs_abd_prealloc_percent = ks->zfs_abd_prealloc_percent.value.ui32;
 
 #ifdef _KERNEL
 		if (ks->zfs_total_memory_limit.value.ui64 > total_memory &&
@@ -731,6 +732,7 @@ arc_kstat_update_windows(kstat_t *ksp, int rw)
 		ks->arc_zfs_arc_average_blocksize.value.ui64 =
 		    zfs_arc_average_blocksize;
 		ks->zvol_io_threads.value.ui32 = zvol_threads;
+		ks->zfs_abd_prealloc_percent.value.ui32 = zfs_abd_prealloc_percent;
 
 #ifdef _KERNEL
 		ks->zfs_total_memory_limit.value.ui64 = total_memory;
diff --git a/module/os/windows/zfs/zfs_kstat_windows.c b/module/os/windows/zfs/zfs_kstat_windows.c
index 36799e2fdd40..1a11d72524d4 100644
--- a/module/os/windows/zfs/zfs_kstat_windows.c
+++ b/module/os/windows/zfs/zfs_kstat_windows.c
@@ -173,7 +173,8 @@ windows_kstat_t windows_kstat = {
 	{ "zfs_total_memory_limit",		KSTAT_DATA_UINT64 },
 	{ "zfs_removal_suspend_progress",	KSTAT_DATA_INT32 },
 	{ "cpu_avx_supported",			KSTAT_DATA_UINT32 },
-	{ "zvol_io_threads",			KSTAT_DATA_UINT32 }
+	{ "zvol_io_threads",			KSTAT_DATA_UINT32 },
+	{ "zfs_abd_prealloc_percent",		KSTAT_DATA_UINT32 },
 };
 
 
@@ -383,6 +384,8 @@ windows_kstat_update(kstat_t *ksp, int rw)
 		    ks->zfs_removal_suspend_progress.value.i32;
 		cpu_avx_supported =
 		    ks->cpu_avx_supported.value.ui32;
+		zfs_abd_prealloc_percent =
+		    ks->zfs_abd_prealloc_percent.value.ui32;
 	} else {
 
 		/* kstat READ */
@@ -573,6 +576,8 @@ windows_kstat_update(kstat_t *ksp, int rw)
 		    cpu_avx_supported;
 		ks->zvol_io_threads.value.ui32 =
 		    zvol_threads;
+		ks->zfs_abd_prealloc_percent.value.ui32 =
+		    zfs_abd_prealloc_percent;
 	}
 	arc_kstat_update_windows(ksp, rw);
 	return (0);
diff --git a/module/os/windows/zfs/zvol_os.c b/module/os/windows/zfs/zvol_os.c
index 0500d2fdffc7..c52a08f6a814 100644
--- a/module/os/windows/zfs/zvol_os.c
+++ b/module/os/windows/zfs/zvol_os.c
@@ -46,6 +46,7 @@ unsigned int zvol_request_sync = 0;
 unsigned int zvol_prefetch_bytes = (128 * 1024);
 unsigned long zvol_max_discard_blocks = 16384;
 int zvol_threads = 0;
+int zfs_abd_prealloc_percent = 10;
 
 taskq_t *zvol_taskq;
 

From df523e26f0f50d68534ddd02608c1680668d77ee Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Tue, 6 Jan 2026 18:53:05 +0530
Subject: [PATCH 03/13] Disabled memory pressure thread

---
 module/os/windows/spl/spl-kmem.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/module/os/windows/spl/spl-kmem.c b/module/os/windows/spl/spl-kmem.c
index 1ebd03d777c9..31126c7ce532 100644
--- a/module/os/windows/spl/spl-kmem.c
+++ b/module/os/windows/spl/spl-kmem.c
@@ -4304,7 +4304,10 @@ spl_free_set_pressure(int64_t new_p)
 		// and any spl_free_set_and_wait_pressure() threads
 		cv_broadcast(&spl_free_thread_cv);
 	}
-	spl_free_last_pressure = zfs_lbolt();
+	if (new_p > 0)
+		spl_free_last_pressure = zfs_lbolt();
+	else
+		spl_free_last_pressure = zfs_lbolt();
 }
 
 void
@@ -4480,6 +4483,7 @@ spl_free_thread()
 		    spl_vm_pressure_level != MAGIC_PRESSURE_UNAVAILABLE) {
 			/* there is pressure */
 			lowmem = true;
+			KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "spl_vm_pressure_level: %lu\n",spl_vm_pressure_level));
 			new_spl_free = -(2LL * PAGE_SIZE * spl_vm_pages_wanted);
 			if (spl_vm_pressure_level > 1) {
 				emergency_lowmem = true;
@@ -4534,6 +4538,7 @@ spl_free_thread()
 			int64_t old_pressure = spl_free_manual_pressure;
 			new_spl_free -= old_pressure * 2LL;
 			lowmem = true;
+			KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "spl_free_manual_pressure: %llu\n",spl_free_manual_pressure));
 			if (spl_free_fast_pressure) {
 				emergency_lowmem = true;
 				new_spl_free -= old_pressure * 4LL;
@@ -4631,6 +4636,7 @@ spl_free_thread()
 			new_spl_free += bminus;
 			lowmem = true;
 			emergency_lowmem = true;
+			KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "spl_vm_pages_wanted %lu\n", spl_vm_pages_wanted));
 			// atomic swaps to set these variables used in arc.c
 			int64_t previous_highest_pressure = 0;
 			int64_t new_p = -bminus;
@@ -4651,6 +4657,7 @@ spl_free_thread()
 			new_spl_free -= bytes_wanted;
 			if (reserve_low && !early_lots_free) {
 				lowmem = true;
+				KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "spl_vm_pages_wanted: %lu reserve_low: %lu early_lots_free: %lu\n", spl_vm_pages_wanted, reserve_low, early_lots_free));
 				if (recent_lowmem == 0) {
 					recent_lowmem = time_now;
 				}
@@ -4761,6 +4768,7 @@ spl_free_thread()
 			    real_total_memory) > 75) {
 				new_spl_free -= total_mem_used / 32;
 				lowmem = true;
+				KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "segkmem_total_mem_allocated: %llu real_total_memory: %llu\n", segkmem_total_mem_allocated, real_total_memory));
 			}
 		}
 
@@ -5393,8 +5401,8 @@ spl_kmem_thread_init(void)
 	(void) thread_create(NULL, 0, spl_free_thread, 0, 0, 0, 0, 92);
 	spl_free_thread_running = TRUE;
 
-	spl_event_thread_exit = FALSE;
-	(void) thread_create(NULL, 0, spl_event_thread, 0, 0, 0, 0, 92);
+	//spl_event_thread_exit = FALSE;
+	//(void) thread_create(NULL, 0, spl_event_thread, 0, 0, 0, 0, 92);
 
 	spl_abd_prealloc_thread_exit = FALSE;
 	(void) thread_create(NULL, 0, spl_abd_prealloc_thread, 0, 0, 0, 0, 92);

From db57b31ca204e21ca2de8d19bdd5bd207fb34395 Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Wed, 7 Jan 2026 11:27:40 +0530
Subject: [PATCH 04/13] Changed abd_cache alloc size

---
 module/os/windows/zfs/abd_os.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/module/os/windows/zfs/abd_os.c b/module/os/windows/zfs/abd_os.c
index 08cefa3c57e1..c0a181d9f395 100644
--- a/module/os/windows/zfs/abd_os.c
+++ b/module/os/windows/zfs/abd_os.c
@@ -87,7 +87,7 @@ struct {
  * will cause the machine to panic if you change it and try to access the data
  * within a scattered ABD.
  */
-size_t zfs_abd_chunk_size = 4096;
+size_t zfs_abd_chunk_size = 65536;
 
 kmem_cache_t *abd_chunk_cache;
 static kstat_t *abd_ksp;

From 85312c2f79459224aa8ededd96ef65dc627de48c Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Thu, 8 Jan 2026 10:33:24 +0530
Subject: [PATCH 05/13] skip source free when the reserved memory is not
 crossing arc_max

---
 module/os/windows/spl/spl-vmem.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/module/os/windows/spl/spl-vmem.c b/module/os/windows/spl/spl-vmem.c
index 2540dca395aa..1bc95dc7b355 100644
--- a/module/os/windows/spl/spl-vmem.c
+++ b/module/os/windows/spl/spl-vmem.c
@@ -448,6 +448,7 @@ uint64_t spl_frag_walk_cnt = 0;
 extern void spl_free_set_emergency_pressure(int64_t p);
 extern uint64_t segkmem_total_mem_allocated;
 extern uint64_t total_memory;
+extern uint64_t zfs_arc_max;
 
 /*
  * Get a vmem_seg_t from the global segfree list.
@@ -1732,12 +1733,23 @@ vmem_xfree(vmem_t *vmp, void *vaddr, size_t size)
 		vsp = vprev;
 	}
 
+	// calling vm_source_free will free the memory to windows, we
+	// don;t want to do this unless we are near the arc limit
+	boolean_t skip_sfree = true;
+	if (segkmem_total_mem_allocated >
+		(zfs_arc_max * 90) / 100) {
+		KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL,
+		       	"vmem_xfree: skip source free segkmem_total_mem_allocated: %llu zfs_arc_max: %llu\n",
+			segkmem_total_mem_allocated, zfs_arc_max));
+		skip_sfree = false;
+        }
+
 	/*
 	 * If the entire span is free, return it to the source.
 	 */
 	if (vsp->vs_aprev->vs_import && vmp->vm_source_free != NULL &&
 	    vsp->vs_aprev->vs_type == VMEM_SPAN &&
-	    vsp->vs_anext->vs_type == VMEM_SPAN) {
+	    vsp->vs_anext->vs_type == VMEM_SPAN && !skip_sfree) {
 		vaddr = (void *)vsp->vs_start;
 		size = VS_SIZE(vsp);
 		ASSERT(size == VS_SIZE(vsp->vs_aprev));

From 3a718c01ef4f30299833e537b9baf324f13bbb80 Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Thu, 8 Jan 2026 18:36:04 +0530
Subject: [PATCH 06/13] skip source free when the reserved memory is not
 crossing arc_max

---
 module/os/windows/spl/spl-vmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/module/os/windows/spl/spl-vmem.c b/module/os/windows/spl/spl-vmem.c
index 1bc95dc7b355..169150550298 100644
--- a/module/os/windows/spl/spl-vmem.c
+++ b/module/os/windows/spl/spl-vmem.c
@@ -1737,7 +1737,7 @@ vmem_xfree(vmem_t *vmp, void *vaddr, size_t size)
 	// don;t want to do this unless we are near the arc limit
 	boolean_t skip_sfree = true;
 	if (segkmem_total_mem_allocated >
-		(zfs_arc_max * 90) / 100) {
+		(zfs_arc_max * 100) / 100) {
 		KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL,
 		       	"vmem_xfree: skip source free segkmem_total_mem_allocated: %llu zfs_arc_max: %llu\n",
 			segkmem_total_mem_allocated, zfs_arc_max));

From cd0c019e143e5305b4e1f9644d2e457c2ac23557 Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Fri, 9 Jan 2026 10:09:42 +0530
Subject: [PATCH 07/13] skip source free when the reserved memory is not
 crossing arc_max

---
 module/os/windows/spl/spl-kmem.c | 4 ++--
 module/os/windows/spl/spl-vmem.c | 5 +----
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/module/os/windows/spl/spl-kmem.c b/module/os/windows/spl/spl-kmem.c
index 31126c7ce532..148b208e2b49 100644
--- a/module/os/windows/spl/spl-kmem.c
+++ b/module/os/windows/spl/spl-kmem.c
@@ -4968,8 +4968,8 @@ spl_abd_prealloc_thread(void *notused)
 	spl_abd_prealloc_thread_exit = FALSE;
 	dprintf("SPL: %s thread_exit\n", __func__);
 
-	KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "SPL: abd prealloc done segkmem_total_mem_allocated: %lld total_memory: %lld zfs_prealloc_percent: %d%\n",
-	    segkmem_total_mem_allocated, total_memory, zfs_abd_prealloc_percent));
+	KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "SPL: abd prealloc done segkmem_total_mem_allocated: %lld total_memory: %lld zfs_arc_max: %llu zfs_prealloc_percent: %d%\n",
+	    segkmem_total_mem_allocated, total_memory, zfs_arc_max, zfs_abd_prealloc_percent));
 	thread_exit();
 }
 
diff --git a/module/os/windows/spl/spl-vmem.c b/module/os/windows/spl/spl-vmem.c
index 169150550298..8bfcc0966193 100644
--- a/module/os/windows/spl/spl-vmem.c
+++ b/module/os/windows/spl/spl-vmem.c
@@ -1737,10 +1737,7 @@ vmem_xfree(vmem_t *vmp, void *vaddr, size_t size)
 	// don;t want to do this unless we are near the arc limit
 	boolean_t skip_sfree = true;
 	if (segkmem_total_mem_allocated >
-		(zfs_arc_max * 100) / 100) {
-		KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL,
-		       	"vmem_xfree: skip source free segkmem_total_mem_allocated: %llu zfs_arc_max: %llu\n",
-			segkmem_total_mem_allocated, zfs_arc_max));
+		(zfs_arc_max * 102) / 100) {
 		skip_sfree = false;
         }
 

From 04d51c1cfab01ae93e1d44b533747c3c79d26473 Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Fri, 9 Jan 2026 19:57:52 +0530
Subject: [PATCH 08/13] Changed the registry name from zfs_abd_prealloc_percent
 to zfs_prealloc_percent Setting zfs_prealloc_percent=0 will disable the
 prealloc feature

---
 include/os/windows/zfs/sys/kstat_windows.h |  4 +-
 module/os/windows/spl/spl-kmem.c           | 34 ++++----
 module/os/windows/spl/spl-vmem.c           | 18 +++--
 module/os/windows/spl/spl-windows.c        | 93 ++++++++++++++++++++++
 module/os/windows/zfs/arc_os.c             |  4 +-
 module/os/windows/zfs/zfs_kstat_windows.c  | 10 +--
 module/os/windows/zfs/zvol_os.c            |  2 +-
 7 files changed, 131 insertions(+), 34 deletions(-)

diff --git a/include/os/windows/zfs/sys/kstat_windows.h b/include/os/windows/zfs/sys/kstat_windows.h
index 3d1a510b9d06..842cc4e006d7 100644
--- a/include/os/windows/zfs/sys/kstat_windows.h
+++ b/include/os/windows/zfs/sys/kstat_windows.h
@@ -150,7 +150,7 @@ typedef struct windows_kstat {
 	kstat_named_t zfs_removal_suspend_progress;
 	kstat_named_t cpu_avx_supported;
 	kstat_named_t zvol_io_threads;
-	kstat_named_t zfs_abd_prealloc_percent;
+	kstat_named_t zfs_prealloc_percent;
 } windows_kstat_t;
 
 
@@ -262,7 +262,7 @@ extern int zfs_autoimport_disable;
 extern int zfs_removal_suspend_progress;
 extern int cpu_avx_supported;
 extern int zvol_threads;
-extern int zfs_abd_prealloc_percent;
+extern int zfs_prealloc_percent;
 
 int  kstat_windows_init(void *);
 void kstat_windows_fini(void);
diff --git a/module/os/windows/spl/spl-kmem.c b/module/os/windows/spl/spl-kmem.c
index 148b208e2b49..a976337e213f 100644
--- a/module/os/windows/spl/spl-kmem.c
+++ b/module/os/windows/spl/spl-kmem.c
@@ -132,6 +132,10 @@ extern uint64_t		zfs_active_rwlock;
 extern uint64_t		total_memory;
 extern uint64_t		real_total_memory;
 
+extern kmem_cache_t *abd_chunk_cache;
+extern uint64_t zfs_arc_max;
+extern int zfs_prealloc_percent;
+
 #define	MULT 1
 
 static const char *KMEM_VA_PREFIX = "kmem_va";
@@ -4304,10 +4308,7 @@ spl_free_set_pressure(int64_t new_p)
 		// and any spl_free_set_and_wait_pressure() threads
 		cv_broadcast(&spl_free_thread_cv);
 	}
-	if (new_p > 0)
-		spl_free_last_pressure = zfs_lbolt();
-	else
-		spl_free_last_pressure = zfs_lbolt();
+	spl_free_last_pressure = zfs_lbolt();
 }
 
 void
@@ -4923,10 +4924,6 @@ spl_event_thread(void *notused)
 	thread_exit();
 }
 
-extern kmem_cache_t *abd_chunk_cache;
-extern uint64_t zfs_arc_max;
-extern int zfs_abd_prealloc_percent;
-
 static void
 spl_abd_prealloc_thread(void *notused)
 {
@@ -4952,13 +4949,14 @@ spl_abd_prealloc_thread(void *notused)
 			delay(hz);
 			continue;
 		}
-		node = (abd_prealloc_node_t *)kmem_cache_alloc(abd_chunk_cache, KM_SLEEP);
-		list_insert_tail(&abd_prealloc_list, node);
 
 		if (segkmem_total_mem_allocated >=
-                    (zfs_arc_max * zfs_abd_prealloc_percent) / 100) {
+                    (zfs_arc_max * zfs_prealloc_percent) / 100) {
                         break;
                 }
+
+		node = (abd_prealloc_node_t *)kmem_cache_alloc(abd_chunk_cache, KM_SLEEP);
+		list_insert_tail(&abd_prealloc_list, node);
 	}
 
 	while ((node = list_remove_head(&abd_prealloc_list)) != NULL) {
@@ -4969,7 +4967,7 @@ spl_abd_prealloc_thread(void *notused)
 	dprintf("SPL: %s thread_exit\n", __func__);
 
 	KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "SPL: abd prealloc done segkmem_total_mem_allocated: %lld total_memory: %lld zfs_arc_max: %llu zfs_prealloc_percent: %d%\n",
-	    segkmem_total_mem_allocated, total_memory, zfs_arc_max, zfs_abd_prealloc_percent));
+	    segkmem_total_mem_allocated, total_memory, zfs_arc_max, zfs_prealloc_percent));
 	thread_exit();
 }
 
@@ -5401,11 +5399,13 @@ spl_kmem_thread_init(void)
 	(void) thread_create(NULL, 0, spl_free_thread, 0, 0, 0, 0, 92);
 	spl_free_thread_running = TRUE;
 
-	//spl_event_thread_exit = FALSE;
-	//(void) thread_create(NULL, 0, spl_event_thread, 0, 0, 0, 0, 92);
-
-	spl_abd_prealloc_thread_exit = FALSE;
-	(void) thread_create(NULL, 0, spl_abd_prealloc_thread, 0, 0, 0, 0, 92);
+	if (zfs_prealloc_percent) {
+		spl_abd_prealloc_thread_exit = FALSE;
+		(void) thread_create(NULL, 0, spl_abd_prealloc_thread, 0, 0, 0, 0, 92);
+	} else {
+		spl_event_thread_exit = FALSE;
+		(void) thread_create(NULL, 0, spl_event_thread, 0, 0, 0, 0, 92);
+	}
 }
 
 void
diff --git a/module/os/windows/spl/spl-vmem.c b/module/os/windows/spl/spl-vmem.c
index 8bfcc0966193..4c3d0a645aea 100644
--- a/module/os/windows/spl/spl-vmem.c
+++ b/module/os/windows/spl/spl-vmem.c
@@ -449,6 +449,7 @@ extern void spl_free_set_emergency_pressure(int64_t p);
 extern uint64_t segkmem_total_mem_allocated;
 extern uint64_t total_memory;
 extern uint64_t zfs_arc_max;
+extern int zfs_prealloc_percent;
 
 /*
  * Get a vmem_seg_t from the global segfree list.
@@ -1734,19 +1735,22 @@ vmem_xfree(vmem_t *vmp, void *vaddr, size_t size)
 	}
 
 	// calling vm_source_free will free the memory to windows, we
-	// don;t want to do this unless we are near the arc limit
-	boolean_t skip_sfree = true;
-	if (segkmem_total_mem_allocated >
-		(zfs_arc_max * 102) / 100) {
-		skip_sfree = false;
-        }
+	// don't want to do this unless we are crossing the arc limit when
+	// zfs_prealloc_percent is enabled.
+	boolean_t allow_vm_source_free = true;
+	if (zfs_prealloc_percent) {
+		if (segkmem_total_mem_allocated <
+			(zfs_arc_max * 102) / 100) {
+			allow_vm_source_free = false;
+		}
+	}
 
 	/*
 	 * If the entire span is free, return it to the source.
 	 */
 	if (vsp->vs_aprev->vs_import && vmp->vm_source_free != NULL &&
 	    vsp->vs_aprev->vs_type == VMEM_SPAN &&
-	    vsp->vs_anext->vs_type == VMEM_SPAN && !skip_sfree) {
+	    vsp->vs_anext->vs_type == VMEM_SPAN && allow_vm_source_free) {
 		vaddr = (void *)vsp->vs_start;
 		size = VS_SIZE(vsp);
 		ASSERT(size == VS_SIZE(vsp->vs_aprev));
diff --git a/module/os/windows/spl/spl-windows.c b/module/os/windows/spl/spl-windows.c
index e6b31edac923..423a6e02c124 100644
--- a/module/os/windows/spl/spl-windows.c
+++ b/module/os/windows/spl/spl-windows.c
@@ -53,12 +53,14 @@ volatile unsigned int vm_page_speculative_count = 5500;
 
 uint64_t spl_GetPhysMem(void);
 uint64_t spl_GetZfsTotalMemory(PUNICODE_STRING RegistryPath);
+uint64_t spl_getZfsPreallocSize(PUNICODE_STRING RegistryPath);
 
 #include <sys/types.h>
 #include <Trace.h>
 
 // Size in bytes of the memory allocated in seg_kmem
 extern uint64_t	segkmem_total_mem_allocated;
+extern int zfs_prealloc_percent;
 #define	MAXHOSTNAMELEN 64
 extern char hostname[MAXHOSTNAMELEN];
 
@@ -528,6 +530,9 @@ spl_start(PUNICODE_STRING RegistryPath)
 	spl_mutex_subsystem_init();
 	spl_kmem_init(total_memory);
 
+	// lets get the registry value now, because the zfs loads the registry little later
+	zfs_prealloc_percent = spl_getZfsPreallocSize(RegistryPath);
+
 	spl_vnode_init();
 	spl_kmem_thread_init();
 	spl_kmem_mp_init();
@@ -755,3 +760,91 @@ spl_GetZfsTotalMemory(PUNICODE_STRING RegistryPath)
 	ZwClose(h);
 	return (newvalue);
 }
+
+uint64_t
+spl_getZfsPreallocSize(PUNICODE_STRING RegistryPath)
+{
+	OBJECT_ATTRIBUTES		ObjectAttributes;
+	HANDLE				h;
+	NTSTATUS			status;
+	uint64_t			newvalue = 0;
+
+	InitializeObjectAttributes(&ObjectAttributes,
+	    RegistryPath,
+	    OBJ_KERNEL_HANDLE | OBJ_CASE_INSENSITIVE,
+	    NULL,
+	    NULL);
+
+	status = ZwOpenKey(&h, // KeyHandle
+	    KEY_ALL_ACCESS, // DesiredAccess
+	    &ObjectAttributes); // ObjectAttributes
+
+	if (!NT_SUCCESS(status)) {
+		dprintf("%s: Unable to open Registry %wZ: 0x%x. "
+		    "Going with defaults.\n", __func__, RegistryPath, status);
+		return (0);
+	}
+
+	ULONG index = 0;
+	ULONG length = 0;
+	PKEY_VALUE_FULL_INFORMATION    regBuffer = NULL;
+
+	for (index = 0; status != STATUS_NO_MORE_ENTRIES; index++) {
+		// Get the buffer size necessary
+		status = ZwEnumerateValueKey(h, index, KeyValueFullInformation,
+		    NULL, 0, &length);
+
+		if ((status != STATUS_BUFFER_TOO_SMALL) &&
+		    (status != STATUS_BUFFER_OVERFLOW))
+			break; // Something is wrong - or we finished
+
+		// Allocate space to hold
+		regBuffer = (PKEY_VALUE_FULL_INFORMATION)ExAllocatePoolWithTag(
+		    NonPagedPoolNx, length, 'zfsr');
+
+		if (regBuffer == NULL)
+			break;
+
+		status = ZwEnumerateValueKey(h, index, KeyValueFullInformation,
+		    regBuffer, length, &length);
+		if (!NT_SUCCESS(status)) {
+			break;
+		}
+		// Convert name to straight ascii so we compare with kstat
+		ULONG outlen = 0;
+		char keyname[KSTAT_STRLEN + 1] = { 0 };
+		status = RtlUnicodeToUTF8N(keyname, KSTAT_STRLEN, &outlen,
+		    regBuffer->Name, regBuffer->NameLength);
+
+		// Conversion failed? move along..
+		if (status != STATUS_SUCCESS && status
+		    != STATUS_SOME_NOT_MAPPED)
+			break;
+
+		// Output string is only null terminated if input is,
+		// so do so now.
+		keyname[outlen] = 0;
+		if (strcasecmp("zfs_prealloc_percent", keyname) == 0) {
+			if (regBuffer->Type != REG_DWORD ||
+			    regBuffer->DataLength != sizeof (uint32_t)) {
+				dprintf("%s: registry '%s' did not match. "
+				    "Type needs to be REG_QWORD. (8 bytes)\n",
+				    __func__, keyname);
+			} else {
+				newvalue = *(uint32_t *)((uint8_t *)regBuffer
+				    + regBuffer->DataOffset);
+				dprintf("%s: zfs_prealloc_percent is set to:"
+				    " %llu\n", __func__, newvalue);
+			}
+			break;
+		}
+		ExFreePool(regBuffer);
+		regBuffer = NULL;
+	}
+
+	if (regBuffer)
+		ExFreePool(regBuffer);
+
+	ZwClose(h);
+	return (newvalue);
+}
diff --git a/module/os/windows/zfs/arc_os.c b/module/os/windows/zfs/arc_os.c
index 60cca3b399ed..6a90d7604c70 100644
--- a/module/os/windows/zfs/arc_os.c
+++ b/module/os/windows/zfs/arc_os.c
@@ -696,7 +696,7 @@ arc_kstat_update_windows(kstat_t *ksp, int rw)
 		zfs_arc_average_blocksize =
 		    ks->arc_zfs_arc_average_blocksize.value.ui64;
 		zvol_threads = ks->zvol_io_threads.value.ui32;
-		zfs_abd_prealloc_percent = ks->zfs_abd_prealloc_percent.value.ui32;
+		zfs_prealloc_percent = ks->zfs_prealloc_percent.value.ui32;
 
 #ifdef _KERNEL
 		if (ks->zfs_total_memory_limit.value.ui64 > total_memory &&
@@ -732,7 +732,7 @@ arc_kstat_update_windows(kstat_t *ksp, int rw)
 		ks->arc_zfs_arc_average_blocksize.value.ui64 =
 		    zfs_arc_average_blocksize;
 		ks->zvol_io_threads.value.ui32 = zvol_threads;
-		ks->zfs_abd_prealloc_percent.value.ui32 = zfs_abd_prealloc_percent;
+		ks->zfs_prealloc_percent.value.ui32 = zfs_prealloc_percent;
 
 #ifdef _KERNEL
 		ks->zfs_total_memory_limit.value.ui64 = total_memory;
diff --git a/module/os/windows/zfs/zfs_kstat_windows.c b/module/os/windows/zfs/zfs_kstat_windows.c
index 1a11d72524d4..8b0c4d9823a3 100644
--- a/module/os/windows/zfs/zfs_kstat_windows.c
+++ b/module/os/windows/zfs/zfs_kstat_windows.c
@@ -174,7 +174,7 @@ windows_kstat_t windows_kstat = {
 	{ "zfs_removal_suspend_progress",	KSTAT_DATA_INT32 },
 	{ "cpu_avx_supported",			KSTAT_DATA_UINT32 },
 	{ "zvol_io_threads",			KSTAT_DATA_UINT32 },
-	{ "zfs_abd_prealloc_percent",		KSTAT_DATA_UINT32 },
+	{ "zfs_prealloc_percent",		KSTAT_DATA_UINT32 },
 };
 
 
@@ -384,8 +384,8 @@ windows_kstat_update(kstat_t *ksp, int rw)
 		    ks->zfs_removal_suspend_progress.value.i32;
 		cpu_avx_supported =
 		    ks->cpu_avx_supported.value.ui32;
-		zfs_abd_prealloc_percent =
-		    ks->zfs_abd_prealloc_percent.value.ui32;
+		zfs_prealloc_percent =
+		    ks->zfs_prealloc_percent.value.ui32;
 	} else {
 
 		/* kstat READ */
@@ -576,8 +576,8 @@ windows_kstat_update(kstat_t *ksp, int rw)
 		    cpu_avx_supported;
 		ks->zvol_io_threads.value.ui32 =
 		    zvol_threads;
-		ks->zfs_abd_prealloc_percent.value.ui32 =
-		    zfs_abd_prealloc_percent;
+		ks->zfs_prealloc_percent.value.ui32 =
+		    zfs_prealloc_percent;
 	}
 	arc_kstat_update_windows(ksp, rw);
 	return (0);
diff --git a/module/os/windows/zfs/zvol_os.c b/module/os/windows/zfs/zvol_os.c
index c52a08f6a814..edcf319f0c07 100644
--- a/module/os/windows/zfs/zvol_os.c
+++ b/module/os/windows/zfs/zvol_os.c
@@ -46,7 +46,7 @@ unsigned int zvol_request_sync = 0;
 unsigned int zvol_prefetch_bytes = (128 * 1024);
 unsigned long zvol_max_discard_blocks = 16384;
 int zvol_threads = 0;
-int zfs_abd_prealloc_percent = 10;
+int zfs_prealloc_percent = 0;
 
 taskq_t *zvol_taskq;
 

From 1b5a18caff3f72807b0dc9fc5be9ad75b3d7cea7 Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Sat, 10 Jan 2026 16:35:20 +0530
Subject: [PATCH 09/13] Reverted zfs_abd_chunk_size from 65536 to 4096 which
 was causing read performace issue

---
 module/os/windows/zfs/abd_os.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/module/os/windows/zfs/abd_os.c b/module/os/windows/zfs/abd_os.c
index c0a181d9f395..08cefa3c57e1 100644
--- a/module/os/windows/zfs/abd_os.c
+++ b/module/os/windows/zfs/abd_os.c
@@ -87,7 +87,7 @@ struct {
  * will cause the machine to panic if you change it and try to access the data
  * within a scattered ABD.
  */
-size_t zfs_abd_chunk_size = 65536;
+size_t zfs_abd_chunk_size = 4096;
 
 kmem_cache_t *abd_chunk_cache;
 static kstat_t *abd_ksp;

From d95a9ef3302a98949ddf9eaa1a957ba577da050a Mon Sep 17 00:00:00 2001
From: Arun KV <arun.kv@datacore.com>
Date: Wed, 1 Apr 2026 15:41:41 +0530
Subject: [PATCH 10/13] Fix spl_thread_create not setting thread priority

---
 include/os/windows/spl/sys/sysmacros.h |  6 +-
 module/os/windows/spl/spl-thread.c     | 82 +++++++++++++++++++++++---
 module/zfs/txg.c                       |  3 +-
 3 files changed, 79 insertions(+), 12 deletions(-)

diff --git a/include/os/windows/spl/sys/sysmacros.h b/include/os/windows/spl/sys/sysmacros.h
index cba1f5fc2d26..e53ae751953d 100644
--- a/include/os/windows/spl/sys/sysmacros.h
+++ b/include/os/windows/spl/sys/sysmacros.h
@@ -81,9 +81,9 @@ extern unsigned int num_ecores;
  * swap priority is at 92. Most ZFS priorities should probably
  * stay below this, but kmem_reap needs to be higher.
  */
-#define	minclsyspri  81 /* BASEPRI_KERNEL */
-#define	defclsyspri  81 /* BASEPRI_KERNEL */
-#define	maxclsyspri  89
+#define	minclsyspri  8 /* BASEPRI_KERNEL */
+#define	defclsyspri  8 /* BASEPRI_KERNEL */
+#define	maxclsyspri  12
 
 #define	NICE_TO_PRIO(nice)		(MAX_RT_PRIO + (nice) + 20)
 #define	PRIO_TO_NICE(prio)		((prio) - MAX_RT_PRIO - 20)
diff --git a/module/os/windows/spl/spl-thread.c b/module/os/windows/spl/spl-thread.c
index 6ef65414c6d4..93cb51557fd8 100644
--- a/module/os/windows/spl/spl-thread.c
+++ b/module/os/windows/spl/spl-thread.c
@@ -39,7 +39,78 @@
 
 uint64_t zfs_threads = 0;
 
-kthread_t *
+
+kthread_t*
+spl_thread_create(
+    caddr_t     stk,
+    size_t      stksize,
+    void        (*proc)(void*),
+    void* arg,
+    size_t      len,
+    int state,
+#ifdef SPL_DEBUG_THREAD
+    char* filename,
+    int line,
+#endif
+    pri_t       pri)
+{
+    NTSTATUS    status;
+    HANDLE      hThread = NULL;
+    PETHREAD    eThread = NULL;
+
+#ifdef SPL_DEBUG_THREAD
+    dprintf("Start thread pri %d\n", pri);
+#endif
+
+    status = PsCreateSystemThread(
+	&hThread,
+	THREAD_ALL_ACCESS,
+	NULL,
+	NULL,
+	NULL,
+	proc,
+	arg);
+
+    if (!NT_SUCCESS(status))
+	return NULL;
+
+    /* Convert HANDLE ETHREAD */
+    status = ObReferenceObjectByHandle(
+	hThread,
+	THREAD_ALL_ACCESS,
+	*PsThreadType,
+	KernelMode,
+	(PVOID*)&eThread,
+	NULL);
+
+    /* We no longer need the handle */
+    ZwClose(hThread);
+
+    if (!NT_SUCCESS(status))
+	return NULL;
+
+    /* Clamp priority to safe Windows range */
+    KPRIORITY newPri = (KPRIORITY)pri;
+
+    if (newPri > maxclsyspri)
+	newPri = maxclsyspri;
+
+    if (newPri < minclsyspri)
+	newPri = minclsyspri;
+
+    /* Set absolute priority */
+    KeSetPriorityThread((PKTHREAD)eThread, newPri);
+
+#ifdef SPL_DEBUG_THREAD
+    dprintf("Thread created with priority %d\n", newPri);
+#endif
+
+    atomic_inc_64(&zfs_threads);
+
+    return (kthread_t*)eThread;
+}
+
+/*kthread_t*
 spl_thread_create(
     caddr_t	stk,
     size_t	stksize,
@@ -72,12 +143,7 @@ spl_thread_create(
 	if (result != STATUS_SUCCESS)
 		return (NULL);
 
-	/*
-	 * Improve the priority when asked to do so
-	 * Thread priorities range from 0 to 31, where 0 is the lowest
-	 * priority and 31 is the highest
-	 */
-
+	
 	if (pri > minclsyspri) {
 		// thread_precedence_policy_data_t policy;
 		// policy.importance = pri - minclsyspri;
@@ -102,7 +168,7 @@ spl_thread_create(
 	ObDereferenceObject(eThread);
 	ZwClose(thread);
 	return ((kthread_t *)eThread);
-}
+}*/
 
 kthread_t *
 spl_current_thread(void)
diff --git a/module/zfs/txg.c b/module/zfs/txg.c
index 46c3bb1bcd0b..ead8d7bc8832 100644
--- a/module/zfs/txg.c
+++ b/module/zfs/txg.c
@@ -213,8 +213,9 @@ txg_sync_start(dsl_pool_t *dp)
 	 * 32-bit x86.  This is due in part to nested pools and
 	 * scrub_visitbp() recursion.
 	 */
+
 	tx->tx_sync_thread = thread_create(NULL, 0, txg_sync_thread,
-	    dp, 0, &p0, TS_RUN, defclsyspri);
+	    dp, 0, &p0, TS_RUN, maxclsyspri);
 
 	mutex_exit(&tx->tx_sync_lock);
 }

From d773f2f5d5db37073c7d7bdde264ad40a9a53a8e Mon Sep 17 00:00:00 2001
From: Pankaj Sharma <pankaj.sharma@datacore.com>
Date: Thu, 16 Apr 2026 22:44:53 -0700
Subject: [PATCH 11/13] Change memory available logic and manual pressure

---
 module/os/windows/spl/spl-kmem.c | 2 +-
 module/os/windows/zfs/arc_os.c   | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/module/os/windows/spl/spl-kmem.c b/module/os/windows/spl/spl-kmem.c
index a976337e213f..48c680ee2672 100644
--- a/module/os/windows/spl/spl-kmem.c
+++ b/module/os/windows/spl/spl-kmem.c
@@ -4235,7 +4235,7 @@ spl_free_wrapper(void)
 int64_t
 spl_free_manual_pressure_wrapper(void)
 {
-	return (spl_free_manual_pressure);
+	return (0);
 }
 
 uint64_t
diff --git a/module/os/windows/zfs/arc_os.c b/module/os/windows/zfs/arc_os.c
index 6a90d7604c70..0d23f80677e2 100644
--- a/module/os/windows/zfs/arc_os.c
+++ b/module/os/windows/zfs/arc_os.c
@@ -59,6 +59,7 @@
 #include <sys/kstat_windows.h>
 
 extern arc_stats_t arc_stats;
+extern uint64_t zfs_arc_max;
 
 static kmutex_t			arc_reclaim_lock;
 static kcondvar_t		arc_reclaim_thread_cv;
@@ -127,7 +128,7 @@ arc_free_memory(void)
 int64_t
 arc_available_memory(void)
 {
-	return (arc_free_memory() - arc_sys_free);
+	return (zfs_arc_max - aggsum_value(&arc_sums.arcstat_size));
 }
 
 int
@@ -137,8 +138,7 @@ arc_memory_throttle(spa_t *spa, uint64_t reserve, uint64_t txg)
 	/* possibly wake up arc reclaim thread */
 
 	if (arc_reclaim_in_loop == B_FALSE) {
-		if (spl_free_manual_pressure_wrapper() != 0 ||
-		    !spl_minimal_physmem_p() ||
+		if (!spl_minimal_physmem_p() ||
 		    arc_reclaim_needed()) {
 			cv_signal(&arc_reclaim_thread_cv);
 			kpreempt(KPREEMPT_SYNC);
@@ -798,7 +798,7 @@ arc_prune_async(int64_t adjust)
 int64_t
 arc_available_memory(void)
 {
-	return (arc_free_memory() - arc_sys_free);
+	return (zfs_arc_max - aggsum_value(&arc_sums.arcstat_size));  
 }
 
 int

From 5f7c0c2d47f6f1aa5a402a31332d90bbb94bc48b Mon Sep 17 00:00:00 2001
From: Pankaj Sharma <pankaj.sharma@datacore.com>
Date: Tue, 28 Apr 2026 02:35:59 -0700
Subject: [PATCH 12/13] Add dynamic zfs_dirty_data_max adjustments

---
 module/zfs/txg.c | 210 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 210 insertions(+)

diff --git a/module/zfs/txg.c b/module/zfs/txg.c
index ead8d7bc8832..75957b765f84 100644
--- a/module/zfs/txg.c
+++ b/module/zfs/txg.c
@@ -113,6 +113,203 @@ static void txg_quiesce_thread(void *arg);
 
 int zfs_txg_timeout = 1;	/* max seconds worth of delta per txg */
 
+#define DIRTY_FLOOR_BYTES       (153ULL << 20)
+#define DIRTY_CEIL_BYTES        (4ULL << 30)
+uint_t zfs_adc_target_sync_pct = 75;
+/* PID gains, all scaled ×1000 to avoid floating point */
+int zfs_adc_kp = 200;   /* Proportional: main corrective force    */
+int zfs_adc_ki = 15;    /* Integral: eliminates steady-state bias  */
+int zfs_adc_kd = 100;   /* Derivative: damping against oscillation */
+
+/* EMA smoothing window in TXG count */
+uint_t zfs_adc_ema_alpha_pct = 25;  /* 25% weight on new sample   */
+/* Minimum TXGs between dirty_max updates (anti-flapping) */
+uint_t zfs_adc_holdoff_txgs = 2;
+/* Master enable — 0 reverts to stock ZFS behavior instantly */
+int zfs_adc_enable = 1;
+
+typedef struct {
+    /* PID state */
+    int64_t     adc_integral;       /* accumulated error (I term)  */
+    int64_t     adc_prev_error;     /* last error sample (D term)  */
+    clock_t     adc_ema_delta;      /* smoothed spa_sync duration  */
+    uint64_t    adc_last_txg;       /* TXG of last adjustment      */
+
+    /* Bounds in bytes, computed once from physmem */
+    uint64_t    adc_min_dirty;
+    uint64_t    adc_max_dirty;
+
+    /* Diagnostics / kstat shadow */
+    uint64_t    adc_n_syncs;        /* total TXGs observed         */
+    uint64_t    adc_n_raised;       /* times dirty_max was raised  */
+    uint64_t    adc_n_lowered;      /* times dirty_max was lowered */
+    uint64_t    adc_n_clamped;      /* times a bound was hit       */
+    int64_t     adc_last_p;         /* last P term for debug       */
+    int64_t     adc_last_i;         /* last I term for debug       */
+    int64_t     adc_last_d;         /* last D term for debug       */
+} txg_adc_t;
+
+static inline clock_t
+adc_ema(clock_t prev, clock_t sample, uint_t alpha_pct)
+{
+    return (prev + (clock_t)(((int64_t)sample - prev)
+	* alpha_pct / 100));
+}
+
+static void
+adc_init(txg_adc_t* adc, clock_t target_ticks)
+{    
+    bzero(adc, sizeof(*adc));
+
+    adc->adc_min_dirty = DIRTY_FLOOR_BYTES;
+    adc->adc_max_dirty = DIRTY_CEIL_BYTES;
+
+    /* Defensive: ensure min < max regardless of tunable misconfiguration */
+    if (adc->adc_min_dirty >= adc->adc_max_dirty)
+	adc->adc_min_dirty = adc->adc_max_dirty / 8;
+
+    /* Seed EMA at target — controller starts in steady state */
+    adc->adc_ema_delta = target_ticks;
+    adc->adc_prev_error = 0;
+    adc->adc_integral = 0;
+}
+
+static void
+adc_update(txg_adc_t* adc, uint64_t txg,
+    clock_t raw_delta, clock_t target_ticks)
+{
+    int64_t  error;         /* normalized error × 1000             */
+    int64_t  p_term;        /* proportional correction             */
+    int64_t  i_term;        /* integral correction                 */
+    int64_t  d_term;        /* derivative correction               */
+    int64_t  pid_out;       /* combined PID output                 */
+    int64_t  adjustment;    /* byte delta for dirty_max            */
+    uint64_t cur, proposed, next;
+
+    adc->adc_n_syncs++;
+
+    /* Step 1: Update smoothed sync duration via EMA */
+    adc->adc_ema_delta = adc_ema(adc->adc_ema_delta,
+	raw_delta, zfs_adc_ema_alpha_pct);
+
+    /* Step 2: Enforce adjustment holdoff (anti-flapping) */
+    if (adc->adc_last_txg != 0 &&
+	(txg - adc->adc_last_txg) < zfs_adc_holdoff_txgs)
+	return;
+
+    /* Step 3: Compute normalized error
+     *
+     * error = (ema_delta - target) / target × 1000
+     *
+     *  > 0 : sync taking too long → dirty_max too high → must shrink
+     *  < 0 : sync finishing early → dirty_max too low  → can grow
+     *  = 0 : perfect operating point
+     *
+     * Example: ema=6s, target=5s → error = +200 (20% over)
+     * Example: ema=3s, target=5s → error = -400 (40% under)
+     */
+    if (target_ticks == 0)
+	return; /* Safety: avoid divide-by-zero on misconfiguration */
+
+    error = ((int64_t)adc->adc_ema_delta - (int64_t)target_ticks)
+	* 1000LL / (int64_t)target_ticks;
+
+    /* Step 4: P term — immediate response to current error */
+    p_term = (int64_t)zfs_adc_kp * error / 1000LL;
+
+    /* Step 5: I term — accumulate to eliminate steady-state offset
+     *
+     * Anti-windup clamp: prevents integral from growing unboundedly
+     * during sustained overload (e.g., pool degraded, resilver running).
+     * Clamped at ±(30 × Kp) which limits I contribution to ≤3× P max.
+     */
+    adc->adc_integral += error;
+    {
+	int64_t windup_limit = 30LL * (int64_t)zfs_adc_kp;
+	if (adc->adc_integral > windup_limit) adc->adc_integral = windup_limit;
+	if (adc->adc_integral < -windup_limit) adc->adc_integral = -windup_limit;
+    }
+    i_term = (int64_t)zfs_adc_ki * adc->adc_integral / 1000LL;
+
+    /* Step 6: D term — dampen oscillation via rate-of-change */
+    d_term = (int64_t)zfs_adc_kd
+	* (error - adc->adc_prev_error) / 1000LL;
+    adc->adc_prev_error = error;
+
+    /* Save for diagnostics */
+    adc->adc_last_p = p_term;
+    adc->adc_last_i = i_term;
+    adc->adc_last_d = d_term;
+
+    /* Step 7: Combine PID output
+     *
+     * pid_out > 0 → sync was slow → DECREASE dirty_max
+     * pid_out < 0 → sync was fast → INCREASE dirty_max
+     * (sign inversion applied in Step 8)
+     */
+    pid_out = p_term + i_term + d_term;
+
+    if (pid_out == 0)
+	return;
+
+    /* Step 8: Convert PID output to byte adjustment
+     *
+     * adjustment = -(pid_out / 1000) × dirty_max × step_scale
+     *
+     * pid_out is in units of 0.1% so dividing by 1000 gives fraction.
+     * Maximum single-step is capped at 20% of current dirty_max to
+     * prevent catastrophic collapse from one anomalous TXG.
+     */
+    cur = zfs_dirty_data_max;
+
+    adjustment = -((int64_t)cur / 1000LL) * pid_out;
+
+    /* Cap single-step adjustment at ±20% of current dirty_max */
+    {
+	int64_t max_step = (int64_t)(cur / 5);
+	if (adjustment > max_step) adjustment = max_step;
+	if (adjustment < -max_step) adjustment = -max_step;
+    }
+
+    /* Step 9: Apply bounds */
+    proposed = (int64_t)cur + adjustment;
+
+    if (proposed <= adc->adc_min_dirty) {
+	next = adc->adc_min_dirty;
+	adc->adc_n_clamped++;
+    }
+    else if (proposed >= adc->adc_max_dirty) {
+	next = adc->adc_max_dirty;
+	adc->adc_n_clamped++;
+    }
+    else {
+	next = proposed;
+    }
+
+    /* Step 10: Commit — single store, visible to txg_delay() immediately */
+    if (next != cur) {
+	zfs_dirty_data_max = next;
+	adc->adc_last_txg = txg;
+	if (next > cur) adc->adc_n_raised++;
+	else            adc->adc_n_lowered++;
+
+	zfs_dbgmsg("txg_adc txg=%llu ema_delta=%ldms target=%ldms "
+	    "err=%lld P=%lld I=%lld D=%lld "
+	    "dirty_max %lluMB→%lluMB",
+	    (u_longlong_t)txg,
+	    (long)(((uint64_t)adc->adc_ema_delta * 1000ULL) / hz),
+	    (long)(((uint64_t)target_ticks * 1000ULL) / hz),
+	    (longlong_t)error,
+	    (longlong_t)p_term,
+	    (longlong_t)i_term,
+	    (longlong_t)d_term,
+	    (u_longlong_t)(cur >> 20),
+	    (u_longlong_t)(next >> 20));
+    }
+}
+
+
+
 /*
  * Prepare the txg subsystem.
  */
@@ -531,11 +728,18 @@ txg_sync_thread(void *arg)
 	tx_state_t *tx = &dp->dp_tx;
 	callb_cpr_t cpr;
 	clock_t start, delta;
+	txg_adc_t    adc;
 
 	(void) spl_fstrans_mark();
 	txg_thread_enter(tx, &cpr);
 
 	start = delta = 0;
+	clock_t adc_target = (clock_t)(zfs_txg_timeout * hz)
+	    * zfs_adc_target_sync_pct / 100;
+
+	if (zfs_adc_enable)
+	    adc_init(&adc, adc_target);
+
 	for (;;) {
 		clock_t timeout = zfs_txg_timeout * hz;
 		clock_t timer;
@@ -599,6 +803,12 @@ txg_sync_thread(void *arg)
 		delta = ddi_get_lbolt() - start;
 		spa_txg_history_fini_io(spa, ts);
 
+		if (zfs_adc_enable) {
+		    adc_target = (clock_t)(zfs_txg_timeout * hz)
+			* zfs_adc_target_sync_pct / 100;
+		    adc_update(&adc, txg, delta, adc_target);
+		}
+
 		mutex_enter(&tx->tx_sync_lock);
 		tx->tx_synced_txg = txg;
 		tx->tx_syncing_txg = 0;

From 1987bd9998de261c8ed58fa86b9e6a03249f5bd3 Mon Sep 17 00:00:00 2001
From: Pankaj Sharma <pankaj.sharma@datacore.com>
Date: Tue, 28 Apr 2026 02:37:35 -0700
Subject: [PATCH 13/13] Remove extra line

---
 module/zfs/txg.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/module/zfs/txg.c b/module/zfs/txg.c
index 75957b765f84..a940770c45bf 100644
--- a/module/zfs/txg.c
+++ b/module/zfs/txg.c
@@ -307,9 +307,6 @@ adc_update(txg_adc_t* adc, uint64_t txg,
 	    (u_longlong_t)(next >> 20));
     }
 }
-
-
-
 /*
  * Prepare the txg subsystem.
  */