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charset=utf-8 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 307DE1C000A X-Stat-Signature: tz433xubo69ka6i6zk7an1wus4m71dcq X-HE-Tag: 1774424193-21231 X-HE-Meta: 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 p/rYvsUV 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 25 March 2026 01:16:52 GMT, SeongJae Park wrote: >Forwarding Sashiko review for doing discussions via mails=2E > ># review url: https://sashiko=2Edev/#/patchset/20260324154005=2E83651-1-o= bjecting@objecting=2Eorg ># start of sashiko=2Edev inline review >commit ff5e227a18cd69435749b0aae0dc2c762c4f0a47 >Author: Josh Law > >mm/damon/core: eliminate hot-path integer division in damon_max_nr_access= es() > =20 >Hardware integer division is slow=2E The function damon_max_nr_accesses()= , >which is called very frequently, performs an integer division=2E >However, the struct damon_attrs already caches this exact ratio in the >internal field aggr_samples=2E We can eliminate the hardware division in >the hot path by simply returning aggr_samples=2E > >> diff --git a/include/linux/damon=2Eh b/include/linux/damon=2Eh >> index d9a3babbafc1=2E=2E04c8a052fcfb 100644 >> --- a/include/linux/damon=2Eh >> +++ b/include/linux/damon=2Eh >> @@ -978,8 +978,7 @@ static inline bool damon_target_has_pid(const struc= t damon_ctx *ctx) >> static inline unsigned int damon_max_nr_accesses(const struct damon_at= trs *attrs) >> { >> /* {aggr,sample}_interval are unsigned long, hence could overflow */ >> - return min(attrs->aggr_interval / attrs->sample_interval, >> - (unsigned long)UINT_MAX); >> + return min_t(unsigned long, attrs->aggr_samples, UINT_MAX); >> } > >If an administrator dynamically updates aggr_interval via sysfs and commi= ts >the inputs, will attrs->aggr_samples be correctly recalculated? > >If aggr_samples becomes stale, kdamond_fn() will compute the real aggrega= tion >loop count and allow r->nr_accesses to increment up to the new bounds (fo= r >example, 80 loops)=2E Meanwhile, damon_max_nr_accesses() will return the >stale aggr_samples cache (for example, 20)=2E > >When evaluating schemes, damon_hot_score() normalizes r->nr_accesses agai= nst >this stale maximum, producing a freq_subscore that severely exceeds >DAMON_MAX_SUBSCORE=2E This causes the calculated hotness to exceed >DAMOS_MAX_SCORE=2E > >For DAMOS_PAGEOUT actions used by damon_reclaim, damon_cold_score() retur= ns >DAMOS_MAX_SCORE - hotness, yielding a highly negative score=2E > >Could this negative score cause an out-of-bounds write on the >kernel heap when used as an array index? > >mm/damon/core=2Ec:damos_walk() { > =2E=2E=2E > c->regions_score_histogram[score] +=3D damon_sz_region(r); > =2E=2E=2E >} > >> diff --git a/mm/damon/core=2Ec b/mm/damon/core=2Ec >> index db6c67e52d2b=2E=2Eafb058f7da5c 100644 >> --- a/mm/damon/core=2Ec >> +++ b/mm/damon/core=2Ec >> @@ -587,6 +587,7 @@ struct damon_ctx *damon_new_ctx(void) >> ctx->attrs=2Esample_interval =3D 5 * 1000; >> ctx->attrs=2Eaggr_interval =3D 100 * 1000; >> ctx->attrs=2Eops_update_interval =3D 60 * 1000 * 1000; >> + ctx->attrs=2Eaggr_samples =3D 20; > >Since this value is cached here, but not updated when intervals change, d= oes >it remain permanently stale during dynamic updates? > > ># end of sashiko=2Edev inline review ># review url: https://sashiko=2Edev/#/patchset/20260324154005=2E83651-1-o= bjecting@objecting=2Eorg ># ># hkml [1] generated a draft of this mail=2E It can be regenerated ># using below command: ># ># hkml patch sashiko_dev --for_forwarding \ ># 20260324154005=2E83651-1-objecting@objecting=2Eorg ># ># [1] https://github=2Ecom/sjp38/hackermail > >Sent using hkml (https://github=2Ecom/sjp38/hackermail) So it's nacked? Or is it just a review V/R Josh Law