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b=POPZCRVTopIVD6QueeAp/dbl/2w0eQjppiua1Xgapd3r3bYqxeOThVbyppGzpk+Ua FdxU9T/jq3b0gprHOqC08n2+VSwbkSBFDcXCv/mm8c9ZF9Zaq1use1gra0+sx/neEK 9mZuxnkBuRKpHgwau3IiHViu0chKTSycGzEVW5YYuTfNPfGXSkD5q+YON8/dPfypzD YA7884+MinfTyzde+PG6yLPhO9XUZXFjPbF6uRZiXKo+1j+jGn3CemPeBGvzRjbkJ0 Fno1psmye9lcBTBlPAMduLnRV7SnTFfNAT3v7CMc+eWrQEHmxsHMSOZ8B33jWPfSCl 7ld4as1g2mg4A== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, Liew Rui Yan , Andrew Morton , SeongJae Park , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 6.6.y v3 2/2] mm/damon/core: fix unconditionally skip last region Date: Fri, 9 Oct 2026 06:49:49 -0700 Message-ID: <20261009134949.11507-3-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261009134949.11507-1-sj@kernel.org> References: <2026092948-moonrise-persecute-3597@gregkh> <20261009134949.11507-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1033F20009 X-Stat-Signature: bsis9odyzwj1f8ep1ehk7iwgaj7ce53j X-HE-Tag: 1791553808-346672 X-HE-Meta: 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 dKCgigzs 9UZmZLVo5lnF00U9lmWxS9gYWFrtwsv0g63BDE1fgVn9DrX7TNbhnmGoPftc5dHJ4pa/4OFFYBB7wFFcsbRN57fXXn1DVNofWtGSoEROU7oc9VXpLD8VqpsN8XgrjosVaX8r6bxIQlsIVBdjZtoELcQnSa0IgGWpmuxlk+pPIZM7rJnWwdvI9/MYIdLgbSdvQXPQkzAo8jPiCMhmKcbhYhzu1vyw8ffJ8VYynDzBEus7axQ03wbhCMRHBP2C7HBqJidBH1tI0wrr3u5jDjSuw5FCxZfb0NCk8Msj1tTF+lRDPH08kUGBVDF8jRg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Liew Rui Yan Once quota set, the charge_{target,addr}_from unconditionally skips and resets at the last region of the tracked target, so the last region can be skipped even when it has not been processed. Example: 1. Target has 2 regions: R1 (0-100 bytes) and R2 (100-200 bytes). 2. Quota is configured to process only 100 bytes per window. 3. Window 1: Processes R1 (0-100). Quota is full. charge_{target, addr}_from is saved at (Target, 100). 4. Window 2: The loop reaches R2. Because R2 is damon_last_region(t), the old code unconditionally returns true, skipping R2 entirely and resetting the charge_{target,addr}_from. Result: R2 is permanently skipped even though it has never been processed. However, it is important to note that this is a very minor issue. This is because it is triggered only when the previous window saved/kept charge_{target,addr}_from, and in the next window, all regions except the last region were skipped by damos_skip_charged_region(). Fix this by only resetting the charge_{target,addr}_from when last region is reached, only skipping when it is applied or cannot split. Link: https://lore.kernel.org/20260908134739.96919-1-sj@kernel.org Fixes: 50585192bc2e ("mm/damon/schemes: skip already charged targets and regions") Signed-off-by: Liew Rui Yan Reviewed-by: SJ Park Signed-off-by: SJ Park Signed-off-by: Andrew Morton Cc: # v5.16.x (cherry picked from commit b3723b596b548c837a766aae3553c14a7b15af2b) Signed-off-by: SJ Park --- mm/damon/core.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index c86cac855b9b..c459eae4bbae 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -884,36 +884,39 @@ static bool damos_skip_charged_region(struct damon_target *t, { struct damos_quota *quota = &s->quota; unsigned long sz_to_skip; + bool skip = false; /* Skip previously charged regions */ if (quota->charge_target_from) { if (t != quota->charge_target_from) return true; - if (r == damon_last_region(t)) { - quota->charge_target_from = NULL; - quota->charge_addr_from = 0; - return true; - } if (quota->charge_addr_from && - r->ar.end <= quota->charge_addr_from) - return true; + r->ar.end <= quota->charge_addr_from) { + skip = true; + goto out; + } if (quota->charge_addr_from && r->ar.start < quota->charge_addr_from) { sz_to_skip = ALIGN_DOWN(quota->charge_addr_from - r->ar.start, DAMON_MIN_REGION); if (!sz_to_skip) { - if (damon_sz_region(r) <= DAMON_MIN_REGION) - return true; + if (damon_sz_region(r) <= DAMON_MIN_REGION) { + skip = true; + goto out; + } sz_to_skip = DAMON_MIN_REGION; } damon_split_region_at(t, r, sz_to_skip); - return true; + skip = true; } + } +out: + if (r == damon_last_region(t)) { quota->charge_target_from = NULL; quota->charge_addr_from = 0; } - return false; + return skip; } static void damos_update_stat(struct damos *s, -- 2.47.3