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Howlett" , Vlastimil Babka , Yu Zhao , Zi Yan , Qi Zheng , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Kairui Song Subject: Re: [PATCH 5/7] mm/mglru: use explicit tier range in read_ctrl_pos() Message-ID: References: <20260818-mglru-flags-cleanup-v1-0-8dbbdac0d28c@tencent.com> <20260818-mglru-flags-cleanup-v1-5-8dbbdac0d28c@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260818-mglru-flags-cleanup-v1-5-8dbbdac0d28c@tencent.com> X-Rspamd-Queue-Id: 8F0A140004 X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: g3tnbdkqcodgisdj4c467mcggfcnsk9u X-HE-Tag: 1787134582-381493 X-HE-Meta: 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 ivJly5GA 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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 08/18/26 at 01:38pm, Kairui Song via B4 Relay wrote: > From: Kairui Song > > read_ctrl_pos() encodes the tier range in a single "tier" parameter > via "tier % MAX_NR_TIERS" as the start and "min(tier, MAX_NR_TIERS-1)" > as the end. This is hard to follow, maintain, or extend. Tier values > 0..3 select a single tier, while tier == MAX_NR_TIERS selects the > full range. > > Replace it with explicit (tier_min, tier_max) parameters using a > closed [tier_min, tier_max] interval, and add LRU_TIER_MIN and > LRU_TIER_MAX for the tier bounds. The call sites now become > self-documenting: > > - get_tier_idx: (LRU_TIER_MIN, LRU_TIER_MIN) for the first tier, > (tier, tier) for each subsequent tier > - get_type_to_scan: (LRU_TIER_MIN, LRU_TIER_MAX) for the full range > > No functional change. > > Signed-off-by: Kairui Song > --- > include/linux/mmzone.h | 2 ++ > mm/vmscan.c | 18 ++++++++++-------- > 2 files changed, 12 insertions(+), 8 deletions(-) To be honest, I like the old version better. The complexity is encapsulated inside the function, and tier_idx can reflect if it's operating on a specific tier or the whole tier. Anyway, this is also good: Reviewed-by: Baoquan He > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 32d9354a754f..d0b5c6217d25 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -492,6 +492,8 @@ enum lruvec_flags { > * folio->flags, masked by LRU_REFS_MASK. > */ > #define MAX_NR_TIERS 4U > +#define LRU_TIER_MIN 0U > +#define LRU_TIER_MAX (MAX_NR_TIERS - 1) > > #ifndef __GENERATING_BOUNDS_H > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a819be6b7ae9..a613bb8d7271 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3198,8 +3198,8 @@ struct ctrl_pos { > int gain; > }; > > -static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain, > - struct ctrl_pos *pos) > +static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier_min, > + int tier_max, int gain, struct ctrl_pos *pos) > { > int i; > struct lru_gen_folio *lrugen = &lruvec->lrugen; > @@ -3208,7 +3208,7 @@ static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain, > pos->gain = gain; > pos->refaulted = pos->total = 0; > > - for (i = tier % MAX_NR_TIERS; i <= min(tier, MAX_NR_TIERS - 1); i++) { > + for (i = tier_min; i <= tier_max; i++) { > pos->refaulted += lrugen->avg_refaulted[type][i] + > atomic_long_read(&lrugen->refaulted[hist][type][i]); > pos->total += lrugen->avg_total[type][i] + > @@ -4804,9 +4804,9 @@ static int get_tier_idx(struct lruvec *lruvec, int type) > * This value is chosen because any other tier would have at least twice > * as many refaults as the first tier. > */ > - read_ctrl_pos(lruvec, type, 0, 2, &sp); > - for (tier = 1; tier < MAX_NR_TIERS; tier++) { > - read_ctrl_pos(lruvec, type, tier, 3, &pv); > + read_ctrl_pos(lruvec, type, LRU_TIER_MIN, LRU_TIER_MIN, 2, &sp); > + for (tier = LRU_TIER_MIN + 1; tier <= LRU_TIER_MAX; tier++) { > + read_ctrl_pos(lruvec, type, tier, tier, 3, &pv); > if (!positive_ctrl_err(&sp, &pv)) > break; > } > @@ -4827,8 +4827,10 @@ static int get_type_to_scan(struct lruvec *lruvec, int swappiness) > * Compare the sum of all tiers of anon with that of file to determine > * which type to scan. > */ > - read_ctrl_pos(lruvec, LRU_GEN_ANON, MAX_NR_TIERS, swappiness, &sp); > - read_ctrl_pos(lruvec, LRU_GEN_FILE, MAX_NR_TIERS, MAX_SWAPPINESS - swappiness, &pv); > + read_ctrl_pos(lruvec, LRU_GEN_ANON, LRU_TIER_MIN, LRU_TIER_MAX, > + swappiness, &sp); > + read_ctrl_pos(lruvec, LRU_GEN_FILE, LRU_TIER_MIN, LRU_TIER_MAX, > + MAX_SWAPPINESS - swappiness, &pv); > > return positive_ctrl_err(&sp, &pv); > } > > -- > 2.55.0 > >