+ mm-damon-sysfs-set-damon_ctx-min_sz_region-only-for-paddr-use-case.patch added to mm-new branch

+ mm-damon-sysfs-set-damon_ctx-min_sz_region-only-for-paddr-use-case.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/sysfs: set damon_ctx->min_sz_region only for paddr use case
has been added to the -mm mm-new branch.  Its filename is
     mm-damon-sysfs-set-damon_ctx-min_sz_region-only-for-paddr-use-case.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-sysfs-set-damon_ctx-min_sz_region-only-for-paddr-use-case.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: SeongJae Park <sj@kernel.org>
Subject: mm/damon/sysfs: set damon_ctx->min_sz_region only for paddr use case
Date: Wed, 17 Sep 2025 08:31:54 -0700

damon_ctx->addr_unit is respected only for physical address space
monitoring use case.  Meanwhile, damon_ctx->min_sz_region is used by the
core layer for aligning regions, regardless of whether it is set for
physical address space monitoring or virtual address spaces monitoring. 
And it is set as 'DAMON_MIN_REGION / damon_ctx->addr_unit'.  Hence, if
user sets ->addr_unit on virtual address spaces monitoring mode, regions
can be unexpectedly aligned in <PAGE_SIZE granularity.  It shouldn't cause
crash-like issues but make monitoring and DAMOS behavior difficult to
understand.

Fix the unexpected behavior by setting ->min_sz_region only when it is
configured for physical address space monitoring.

The issue was found from a result of Chris' experiments that thankfully
shared with me off-list.

Link: https://lkml.kernel.org/r/20250917160041.53187-1-sj@kernel.org
Fixes: d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: ze zuo <zuoze1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/sysfs.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/damon/sysfs.c~mm-damon-sysfs-set-damon_ctx-min_sz_region-only-for-paddr-use-case
+++ a/mm/damon/sysfs.c
@@ -1435,7 +1435,10 @@ static int damon_sysfs_apply_inputs(stru
 	if (err)
 		return err;
 	ctx->addr_unit = sys_ctx->addr_unit;
-	ctx->min_sz_region = max(DAMON_MIN_REGION / sys_ctx->addr_unit, 1);
+	/* addr_unit is respected by only DAMON_OPS_PADDR */
+	if (sys_ctx->ops_id == DAMON_OPS_PADDR)
+		ctx->min_sz_region = max(
+				DAMON_MIN_REGION / sys_ctx->addr_unit, 1);
 	err = damon_sysfs_set_attrs(ctx, sys_ctx->attrs);
 	if (err)
 		return err;
_

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

mm-damon-lru_sort-use-param_ctx-for-damon_attrs-staging.patch
mm-damon-core-reset-age-if-nr_accesses-changes-between-non-zero-and-zero.patch
mm-damon-core-set-effective-quota-on-first-charge-window.patch
docs-mm-damon-maintainer-profile-update-community-meetup-for-reservation-requirements.patch
docs-admin-guide-mm-damon-start-add-target_pid-to-damos-example-command.patch
maintainers-rename-damon-section.patch
mm-damon-core-implement-damon_initialized-function.patch
mm-damon-stat-use-damon_initialized.patch
mm-damon-reclaim-use-damon_initialized.patch
mm-damon-lru_sort-use-damon_initialized.patch
samples-damon-wsse-use-damon_initialized.patch
samples-damon-prcl-use-damon_initialized.patch
samples-damon-mtier-use-damon_initialized.patch
mm-damon-stat-expose-the-current-tuned-aggregation-interval.patch
mm-damon-stat-expose-negative-idle-time.patch
mm-damon-sysfs-set-damon_ctx-min_sz_region-only-for-paddr-use-case.patch