* [RFC PATCH 6.6.y 1/3] mm/damon/core: skip applying scheme if region split for quota fails
2026-11-07 22:21 [RFC PATCH 6.6.y 0/3] mm/damon: porting fixes that cherry-pick failed on 2026-11-07 SJ Park
@ 2026-11-07 22:21 ` SJ Park
2026-11-07 22:22 ` [RFC PATCH 6.6.y 2/3] mm/damon/core: filter out damos address filter-split failed region SJ Park
2026-11-07 22:22 ` [RFC PATCH 6.6.y 3/3] mm/damon/core: remove unreachable damos charge_{target,addr}_from SJ Park
2 siblings, 0 replies; 4+ messages in thread
From: SJ Park @ 2026-11-07 22:21 UTC (permalink / raw)
Cc: SJ Park, stable, Andrew Morton, Usama Arif, damon, linux-kernel,
linux-mm
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.
6.6.y porting notes. Modify damon_split_region_at() to return failures.
It is a part of commit c60874860762 ("mm/damon/core: handle region split
failure in apply_min_nr_regions()"). Without it, build fails.
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: <stable@vger.kernel.org> # 5.16.x
(cherry picked from commit 90c2fa6adfed7abe0935506a43cdff3a05c1fff0)
Signed-off-by: SJ Park <sj@kernel.org>
---
mm/damon/core.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/mm/damon/core.c b/mm/damon/core.c
index b5b6d00d7a3b5..9d4a78deaa06a 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -828,7 +828,7 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
}
}
-static void damon_split_region_at(struct damon_target *t,
+static int damon_split_region_at(struct damon_target *t,
struct damon_region *r, unsigned long sz_r);
static bool __damos_valid_target(struct damon_region *r, struct damos *s)
@@ -1004,7 +1004,8 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
DAMON_MIN_REGION);
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_filter_out(c, t, r, s))
return;
@@ -1266,15 +1267,17 @@ static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold,
*
* r the region to be split
* sz_r size of the first sub-region that will be made
+ *
+ * Return: 0 on success, negative error code otherwise.
*/
-static void damon_split_region_at(struct damon_target *t,
+static int damon_split_region_at(struct damon_target *t,
struct damon_region *r, unsigned long sz_r)
{
struct damon_region *new;
new = damon_new_region(r->ar.start + sz_r, r->ar.end);
if (!new)
- return;
+ return -ENOMEM;
r->ar.end = new->ar.start;
@@ -1283,6 +1286,7 @@ static void damon_split_region_at(struct damon_target *t,
new->nr_accesses = r->nr_accesses;
damon_insert_region(new, r, damon_next_region(r), t);
+ return 0;
}
/* Split every region in the given target into 'nr_subs' regions */
--
2.47.3
^ permalink raw reply [flat|nested] 4+ messages in thread* [RFC PATCH 6.6.y 2/3] mm/damon/core: filter out damos address filter-split failed region
2026-11-07 22:21 [RFC PATCH 6.6.y 0/3] mm/damon: porting fixes that cherry-pick failed on 2026-11-07 SJ Park
2026-11-07 22:21 ` [RFC PATCH 6.6.y 1/3] mm/damon/core: skip applying scheme if region split for quota fails SJ Park
@ 2026-11-07 22:22 ` SJ Park
2026-11-07 22:22 ` [RFC PATCH 6.6.y 3/3] mm/damon/core: remove unreachable damos charge_{target,addr}_from SJ Park
2 siblings, 0 replies; 4+ messages in thread
From: SJ Park @ 2026-11-07 22:22 UTC (permalink / raw)
Cc: SJ Park, stable, Andrew Morton, damon, linux-kernel, linux-mm
When an address type DAMOS filter is configured, DAMOS tries to split the
region for the filter range, and apply DAMOS action to the filter-in
region. The split operation (damon_split_region_at()) could fail from
allocation failure under extreme memory pressure. In the case, DAMOS
action could be applied more or less than expected, ignoring the address
filter.
The issue only rarely happens under extreme memory pressure. No crash or
leak happens. Occasionally not applying the action to a few regions
shouldn't be a real problem. But applying the action to a region that the
user has excluded via address filter could be a surprise depending on the
use case. It is only theoretical. No such real case is found yet.
Filter out the entire region if the split is failed. Update
damos_filter_match() signature to receive the error from split. Also
update kunit tests for the updated signature.
The issue was discovered [1] by sashiko.
Link: https://lore.kernel.org/20261020004119.106690-1-sj@kernel.org
Link: https://lore.kernel.org/20260801203121.117449-1-sj@kernel.org [1]
Fixes: ab9bda001b68 ("mm/damon/core: introduce address range type damos filter")
Signed-off-by: SJ Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org> # 6.6.x
(cherry picked from commit bbeec2d8324d7aac438bb12dd2d22b184e0a8d43)
Signed-off-by: SJ Park <sj@kernel.org>
---
mm/damon/core-test.h | 11 ++++++-----
mm/damon/core.c | 13 +++++++++----
2 files changed, 15 insertions(+), 9 deletions(-)
diff --git a/mm/damon/core-test.h b/mm/damon/core-test.h
index dd91b0eea61ff..1988b7dd29e96 100644
--- a/mm/damon/core-test.h
+++ b/mm/damon/core-test.h
@@ -461,6 +461,7 @@ static void damos_test_filter_out(struct kunit *test)
struct damon_target *t;
struct damon_region *r, *r2;
struct damos_filter *f;
+ int err;
f = damos_new_filter(DAMOS_FILTER_TYPE_ADDR, true);
if (!f)
@@ -482,25 +483,25 @@ static void damos_test_filter_out(struct kunit *test)
damon_add_region(r, t);
/* region in the range */
- KUNIT_EXPECT_TRUE(test, __damos_filter_out(NULL, t, r, f));
+ KUNIT_EXPECT_TRUE(test, __damos_filter_out(NULL, t, r, f, &err));
KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
/* region before the range */
r->ar.start = DAMON_MIN_REGION * 1;
r->ar.end = DAMON_MIN_REGION * 2;
- KUNIT_EXPECT_FALSE(test, __damos_filter_out(NULL, t, r, f));
+ KUNIT_EXPECT_FALSE(test, __damos_filter_out(NULL, t, r, f, &err));
KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
/* region after the range */
r->ar.start = DAMON_MIN_REGION * 6;
r->ar.end = DAMON_MIN_REGION * 8;
- KUNIT_EXPECT_FALSE(test, __damos_filter_out(NULL, t, r, f));
+ KUNIT_EXPECT_FALSE(test, __damos_filter_out(NULL, t, r, f, &err));
KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
/* region started before the range */
r->ar.start = DAMON_MIN_REGION * 1;
r->ar.end = DAMON_MIN_REGION * 4;
- KUNIT_EXPECT_FALSE(test, __damos_filter_out(NULL, t, r, f));
+ KUNIT_EXPECT_FALSE(test, __damos_filter_out(NULL, t, r, f, &err));
/* filter should have split the region */
KUNIT_EXPECT_EQ(test, r->ar.start, DAMON_MIN_REGION * 1);
KUNIT_EXPECT_EQ(test, r->ar.end, DAMON_MIN_REGION * 2);
@@ -515,7 +516,7 @@ static void damos_test_filter_out(struct kunit *test)
/* region started in the range */
r->ar.start = DAMON_MIN_REGION * 2;
r->ar.end = DAMON_MIN_REGION * 8;
- KUNIT_EXPECT_TRUE(test, __damos_filter_out(NULL, t, r, f));
+ KUNIT_EXPECT_TRUE(test, __damos_filter_out(NULL, t, r, f, &err));
/* filter should have split the region */
KUNIT_EXPECT_EQ(test, r->ar.start, DAMON_MIN_REGION * 2);
KUNIT_EXPECT_EQ(test, r->ar.end, DAMON_MIN_REGION * 6);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 9d4a78deaa06a..99e934a6d1ce9 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -930,13 +930,14 @@ static void damos_update_stat(struct damos *s,
}
static bool __damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
- struct damon_region *r, struct damos_filter *filter)
+ struct damon_region *r, struct damos_filter *filter, int *err)
{
bool matched = false;
struct damon_target *ti;
int target_idx = 0;
unsigned long start, end;
+ *err = 0;
switch (filter->type) {
case DAMOS_FILTER_TYPE_TARGET:
damon_for_each_target(ti, ctx) {
@@ -962,12 +963,13 @@ static bool __damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
}
/* start before the range and overlap */
if (r->ar.start < start) {
- damon_split_region_at(t, r, start - r->ar.start);
+ *err = damon_split_region_at(t, r,
+ start - r->ar.start);
matched = false;
break;
}
/* start inside the range */
- damon_split_region_at(t, r, end - r->ar.start);
+ *err = damon_split_region_at(t, r, end - r->ar.start);
matched = true;
break;
default:
@@ -981,9 +983,12 @@ static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
struct damon_region *r, struct damos *s)
{
struct damos_filter *filter;
+ bool matching;
+ int err;
damos_for_each_filter(filter, s) {
- if (__damos_filter_out(ctx, t, r, filter))
+ matching = __damos_filter_out(ctx, t, r, filter, &err);
+ if (matching || err)
return true;
}
return false;
--
2.47.3
^ permalink raw reply [flat|nested] 4+ messages in thread