+ mm-khugepaged-retry-with-sync-writeback-for-madv_collapse.patch added to mm-new branch

+ mm-khugepaged-retry-with-sync-writeback-for-madv_collapse.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/khugepaged: retry with sync writeback for MADV_COLLAPSE
has been added to the -mm mm-new branch.  Its filename is
     mm-khugepaged-retry-with-sync-writeback-for-madv_collapse.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-retry-with-sync-writeback-for-madv_collapse.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

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------------------------------------------------------
From: Shivank Garg <shivankg@amd.com>
Subject: mm/khugepaged: retry with sync writeback for MADV_COLLAPSE
Date: Mon, 15 Dec 2025 08:46:19 +0000

When MADV_COLLAPSE is called on file-backed mappings (e.g., executable
text sections), the pages may still be dirty from recent writes. 
collapse_file() will trigger async writeback and fail with
SCAN_PAGE_DIRTY_OR_WRITEBACK (-EAGAIN).

MADV_COLLAPSE is a synchronous operation where userspace expects immediate
results.  If the collapse fails due to dirty pages, perform synchronous
writeback on the specific range and retry once.

This avoids spurious failures for freshly written executables while
avoiding unnecessary synchronous I/O for mappings that are already clean.

Link: https://lkml.kernel.org/r/20251215084615.5283-7-shivankg@amd.com
Signed-off-by: Shivank Garg <shivankg@amd.com>
Reported-by: Branden Moore <Branden.Moore@amd.com>
Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com
Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE")
Suggested-by: David Hildenbrand <david@kernel.org>
Tested-by: Lance Yang <lance.yang@linux.dev>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: wang lian <lianux.mm@gmail.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/khugepaged.c |   40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

--- a/mm/khugepaged.c~mm-khugepaged-retry-with-sync-writeback-for-madv_collapse
+++ a/mm/khugepaged.c
@@ -22,6 +22,7 @@
 #include <linux/dax.h>
 #include <linux/ksm.h>
 #include <linux/pgalloc.h>
+#include <linux/backing-dev.h>
 
 #include <asm/tlb.h>
 #include "internal.h"
@@ -2787,9 +2788,11 @@ int madvise_collapse(struct vm_area_stru
 	hend = end & HPAGE_PMD_MASK;
 
 	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
+		bool retried = false;
 		int result = SCAN_FAIL;
 
 		if (!mmap_locked) {
+retry:
 			cond_resched();
 			mmap_read_lock(mm);
 			mmap_locked = true;
@@ -2819,6 +2822,43 @@ int madvise_collapse(struct vm_area_stru
 		if (!mmap_locked)
 			*lock_dropped = true;
 
+		/*
+		 * If the file-backed VMA has dirty pages, the scan triggers
+		 * async writeback and returns SCAN_PAGE_DIRTY_OR_WRITEBACK.
+		 * Since MADV_COLLAPSE is sync, we force sync writeback and
+		 * retry once.
+		 */
+		if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !retried) {
+			/*
+			 * File scan drops the lock. We must re-acquire it to
+			 * safely inspect the VMA and hold the file reference.
+			 */
+			if (!mmap_locked) {
+				cond_resched();
+				mmap_read_lock(mm);
+				mmap_locked = true;
+				result = hugepage_vma_revalidate(mm, addr, false, &vma, cc);
+				if (result != SCAN_SUCCEED)
+					goto handle_result;
+			}
+
+			if (!vma_is_anonymous(vma) && vma->vm_file &&
+			    mapping_can_writeback(vma->vm_file->f_mapping)) {
+				struct file *file = get_file(vma->vm_file);
+				pgoff_t pgoff = linear_page_index(vma, addr);
+				loff_t lstart = (loff_t)pgoff << PAGE_SHIFT;
+				loff_t lend = lstart + HPAGE_PMD_SIZE - 1;
+
+				mmap_read_unlock(mm);
+				mmap_locked = false;
+				*lock_dropped = true;
+				filemap_write_and_wait_range(file->f_mapping, lstart, lend);
+				fput(file);
+				retried = true;
+				goto retry;
+			}
+		}
+
 handle_result:
 		switch (result) {
 		case SCAN_SUCCEED:
_

Patches currently in -mm which might be from shivankg@amd.com are

mm-khugepaged-map-dirty-writeback-pages-failures-to-eagain.patch
mm-khugepaged-retry-with-sync-writeback-for-madv_collapse.patch