+ mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.patch added to mm-new branch

+ mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/core: skip applying scheme if region split for quota fails
has been added to the -mm mm-new branch.  Its filename is
     mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: SJ Park <sj@kernel.org>
Subject: mm/damon/core: skip applying scheme if region split for quota fails
Date: Tue, 1 Sep 2026 06:18:42 -0700

Patch series "mm/damon: fix DAMOS bugs in core, paddr and vaddr".

Fix misc bugs of DAMOS.  Patch 1 makes DAMOS less stress memory allocator
under extreme situation.  Patches 2 and 3 fix wrong folios walking in
DAMON_PADDR.  Patches 4 and 5 fix wrong folios walking in DAMON_VADDR. 
Patches 6-8 handle extreme and unlikely memory situations that can cause
divide by zero and underflow.

All bugs are discovered by Sashiko.


This patch (of 8):

damos_apply_scheme() splits a region and apply the action to the subregion
if it is needed for not violating the quota.  The split operation
(damon_split_region_at()) could fail for allocation failure.  In the case,
the quota could be violated.  From the user's perspective, DAMOS becomes
more aggressive than expected under the extreme situation.  Handle the
failure.

The user impact is not critical.  The failure of damon_split_region_at()
is unlikely since it is arguably too small to fail.  Also DAMOS being
aggressive is limited to the single region.  Users can set min_nr_regions
to set the maximum size of each region.  If it is reasonably set, the
transient overhead shouldn't be critical.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260901131850.98037-1-sj@kernel.org
Link: https://lore.kernel.org/20260901131850.98037-2-sj@kernel.org
Link: https://lore.kernel.org/20260718171523.87547-1-sj@kernel.org [1]
Fixes: 2b8a248d5873 ("mm/damon/schemes: implement size quota for schemes application speed control")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/mm/damon/core.c~mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails
+++ a/mm/damon/core.c
@@ -2604,7 +2604,8 @@ static void damos_apply_scheme(struct da
 					c->min_region_sz);
 			if (!sz)
 				goto update_stat;
-			damon_split_region_at(t, r, sz);
+			if (damon_split_region_at(t, r, sz))
+				goto update_stat;
 		}
 		if (damos_core_filter_out(c, t, r, s))
 			return;
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.patch
mm-damon-paddr-respect-folio-end-for-damos_stat.patch
mm-damon-paddr-respect-folio-end-for-damos-actions-except-stat.patch
mm-damon-vaddr-respect-folio-end-for-damos_stat.patch
mm-damon-vaddr-respect-folio-end-for-damos_migrate_hotcold.patch
mm-damon-core-handle-extreme-memory-state-in-damon_get_node_mem_bp.patch
mm-damon-core-handle-extreme-memory-state-in-get_node_memcg_used_bp.patch
mm-damon-core-handle-extreme-memory-state-in-get_in_active_mem_bp.patch