+ mm-mremap-reaccount-on-unmap-failure-only-if-accounted.patch added to mm-new branch

+ mm-mremap-reaccount-on-unmap-failure-only-if-accounted.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/mremap: reaccount on unmap failure only if accounted
has been added to the -mm mm-new branch.  Its filename is
     mm-mremap-reaccount-on-unmap-failure-only-if-accounted.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mremap-reaccount-on-unmap-failure-only-if-accounted.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.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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and is updated there most days

------------------------------------------------------
From: Josef Bacik <josef@toxicpanda.com>
Subject: mm/mremap: reaccount on unmap failure only if accounted
Date: Thu, 05 Nov 2026 14:02:05 +0000

When the unmap of the source range fails at the end of an mremap() move,
the length of the range is charged to vm_committed_as even if the VMA was
never accounted, for example a MAP_SHARED or MAP_NORESERVE mapping. 
Nothing ever uncharges these pages, so each such failure permanently
inflates the committed memory count.

This was reproduced with fault injection: each failure on a shmem mapping
left Committed_AS higher by the size of the moved range after everything
was unmapped.

Fix by charging the range again only when accountable_move is set.

Link: https://lore.kernel.org/20261105-b4-mremap-pre-split-v3-3-f8789de76849@toxicpanda.com
Fixes: b714ccb02a76 ("mm/mremap: complete refactor of move_vma()")
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Sarthak Sharma <sarthak.sharma@arm.com>
---

 mm/mremap.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/mremap.c~mm-mremap-reaccount-on-unmap-failure-only-if-accounted
+++ a/mm/mremap.c
@@ -1246,7 +1246,8 @@ static void unmap_source_vma(struct vma_
 	vrm->vmi_needs_invalidate = true;
 	if (err) {
 		/* OOM: unable to split vma, just get accounts right */
-		vm_acct_memory(len >> PAGE_SHIFT);
+		if (accountable_move)
+			vm_acct_memory(len >> PAGE_SHIFT);
 		return;
 	}
 
_

Patches currently in -mm which might be from josef@toxicpanda.com are

mm-zswap-drop-the-stale-zswap-entry-of-a-zero-folio.patch
mm-swap-account-synchronous-swap-reads-as-memory-stall.patch
mm-mremap-fix-hugetlb-reservation-leak-on-partial-move.patch
selftests-mm-test-a-partial-mremap-of-hugetlb-memory.patch
mm-mremap-reaccount-on-unmap-failure-only-if-accounted.patch
mm-mremap-restore-vma_account_bit-if-the-unmap-fails.patch
selftests-mm-test-mremap-with-an-old-size-of-0.patch
zram-lz4-lz4hc-accept-dictionaries-of-more-than-64-kib.patch