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b=odGA46Dcm3MWSP95DuGe/5RlQEgtLVssOUaGdx3ubKvbhCCpStwmfZpn4bg7+XzS9 itnFZVga+XIkG/VtdWc5YXzrSfeE0Es6u0ctSercDmA4BBLG83vx0F+66lvSKpzaex lDH5YVDxg5FPnbhDU+RmyfZdmknFNL2meOUgMYs/bbIaZmQer3+YW43VDLLtcQrVGM fE9fwiPWIzZEPksTqWzEeOCtS06z6z/WuYjzyDjBWWm73zt7JcyvYzo53ua8OKBgYY 35B6B45v6/uIieQ0nKZkxwpLORJDnN1nQooy6TrxjnJjBH/FjHKuq5jKkQSwRABiC8 cvrC+bIaGG9kg== From: SeongJae Park To: Cc: SeongJae Park , Andrew Morton , damon@lists.linux.dev, kernel-team@meta.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH] mm/damon/core: reset age if nr_accesses changes between non-zero and zero Date: Mon, 8 Sep 2025 20:43:53 -0700 Message-Id: <20250909034353.7064-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 4A556A0006 X-Stat-Signature: j3x18wh9sofxk8m96rkff79imfke7j7r X-Rspam-User: X-HE-Tag: 1757389439-191070 X-HE-Meta: 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 lPIonljM e1TBPwbhl2xRy4VwtoEorplS7tmFBhtTvygR6HC1ym1jjfOWCDMr5NsDXHll0ObQHE2b8KOsh1uJFe2tNJK6G2gLbIDe/pyMmIjNZv24dc2EBOZOn+1mmpzgBREmUSd0AzrRAqO1fLe4FqZLQDi9svASktGs6h8tuV/4Ll2eIDmbNHywYTgH9c6Cgk1DjarAmMJ1rEZ5CT3SPmnUMeM448IKLvgH2qH9RPPX6tdVOeltJz3Glz4HO6uj2FboCcdMBm85EVVQJy/i9+I6uvjy1c8txJg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: DAMON resets the age of a region if its nr_accesses value has significantly changed. Specifically, the threshold is calculated as 20% of largest nr_accesses of the current snapshot. This means that regions changing the nr_accesses from zero to small non-zero value or from a small non-zero value to zero will keep the age. Since many users treat zero nr_accesses regions special, this can be confusing. Kernel code including DAMOS' regions priority calculation and DAMON_STAT's idle time calculation also treat zero nr_accesses regions special. Make it unconfusing by resetting the age when the nr_accesses changes between zero and a non-zero value. Signed-off-by: SeongJae Park --- mm/damon/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index be5942435d78..996647caca02 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2261,6 +2261,9 @@ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres, damon_for_each_region_safe(r, next, t) { if (abs(r->nr_accesses - r->last_nr_accesses) > thres) r->age = 0; + else if ((!r->nr_accesses && r->last_nr_accesses) || + (r->nr_accesses && !r->last_nr_accesses)) + r->age = 0; else r->age++; base-commit: 580b0ae8069448252cfea72b75ba5b0857c128e0 -- 2.39.5