FAILED: patch "[PATCH] mm/damon/core: skip aging from repeated aggressive merging" failed to apply to 5.15-stable tree
Subsystems (3)
[email protected]
maintainerThe patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 0250dbe08c730d003ef9f484da56ae09a1ea0c4c
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090841-retying-object-67ca@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 0250dbe08c730d003ef9f484da56ae09a1ea0c4c Mon Sep 17 00:00:00 2001
From: SJ Park <[email protected]>
Date: Sun, 12 Jul 2026 09:54:30 -0700
Subject: [PATCH] mm/damon/core: skip aging from repeated aggressive merging
The number of DAMON regions could temporarily exceed the user-defined maximum number of regions limit for corner cases. For example, users could lower the limit via runtime parameters update. For such a case, kdamond_merge_regions() repeats merging regions in the case doubling the merge threshold. The repeated merge operation could update the age of regions multiple times. This corrupts the monitoring results. Fix the issue by asking the merge operation to skip aging for the corner case.
The user impact is degradation of the monitoring quality. The impact should be mild, since the degradation is only temporal, and it is not common to happen in realistic setups.
The issue was discovered [1,2] by Sashiko.
mm/damon/core.c +13 -8
@@ -3308,7 +3308,7 @@ static unsigned int damon_merge_score(struct damon_region *r, bool last,* sz_limit size upper limit of each region */ static void damon_merge_regions_of (struct damon_target *t,unsigned int thres, -unsigned long sz_limit,struct damon_ctx *ctx) +unsigned long sz_limit,struct damon_ctx *ctx,bool count_age) {struct damon_region *r, *prev =NULL , *next;bool use_probe_hits =damon_has_probe_weights (ctx);
@@ -3319,12 +3319,14 @@ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres, score =damon_merge_score (r, false, ctx, use_probe_hits); last_score =damon_merge_score (r, true, ctx, use_probe_hits); -if (abs_diff (score, last_score) > thres) - r->age =0 ; -else if ((score ==0 ) != (last_score ==0 )) - r->age =0 ; -else - r->age++; +if (count_age) { +if (abs_diff (score, last_score) > thres) + r->age =0 ; +else if ((score ==0 ) != (last_score ==0 )) + r->age =0 ; +else + r->age++; + }if (!prev) goto set_prev_continue;
@@ -3366,15 +3368,18 @@ static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold,struct damon_target *t;unsigned int nr_regions;unsigned int max_thres; +bool count_age = true; max_thres = c->attrs.aggr_interval / (c->attrs.sample_interval ? c->attrs.sample_interval :1 );do { nr_regions =0 ;damon_for_each_target (t, c) { -damon_merge_regions_of (t, threshold, sz_limit, c); +damon_merge_regions_of (t, threshold, sz_limit, c, + count_age); nr_regions +=damon_nr_regions (t); } + count_age = false; threshold =max (1 , threshold *2 ); }while (nr_regions > c->attrs.max_nr_regions && threshold /2 < max_thres);
mm/damon/tests/core-kunit.h +1 -1
@@ -257,7 +257,7 @@ static void damon_test_merge_regions_of(struct kunit *test)damon_add_region (r, t); } -damon_merge_regions_of (t,9 ,9999 , ctx); +damon_merge_regions_of (t,9 ,9999 , ctx, true);/* 0-112, 114-130, 130-156, 156-170, 170-230, 230-10170 */ KUNIT_EXPECT_EQ (test,damon_nr_regions (t),6u );for (i =0 ; i <6 ; i++) {
SJ Park
maintainerQuoted 5 lines · On Tue, 08 Sep 2026 14:52:42 +0200 <[email protected]> wrote:
The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
[...]
Quoted 19 lines
------------------ original commit in Linus's tree ------------------
From
0250dbe08c730d003ef9f484da56ae09a1ea0c4cMon Sep 17 00:00:00 2001
From: SJ Park <[email protected]>
Date: Sun, 12 Jul 2026 09:54:30 -0700
Subject: [PATCH]mm/damon/core: skip aging from repeated aggressive mergingThe number of DAMON regions could temporarily exceed the user-defined maximum number of regions limit for corner cases. For example, users could lower the limit via runtime parameters update. For such a case,
kdamond_merge_regions()repeats merging regions in the case doubling the merge threshold. The repeated merge operation could update the age of regions multiple times. This corrupts the monitoring results. Fix the issue by asking the merge operation to skip aging for the corner case.The user impact is degradation of the monitoring quality. The impact should be mild, since the degradation is only temporal, and it is not common to happen in realistic setups.
Quoted 6 lines
The issue was discovered [1,2] by Sashiko.
Fixes 310d6c15e910 ("mm/damon/core: merge regions aggressively when max_nr_regions is unmet")
The broken commit is backported to 5.15.y. Seems this patch was tried to be applied on 5.15.y for the reason. However, this fix also depends on commit fda504fade7f ("mm/damon/core: account age of target regions"), which is not in 5.15.y. So, this patch doesn't need to be ported on 5.15.y.
Thanks,
SJ
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