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Mon, 23 Mar 2026 23:05:16 -0700 (PDT) Date: Tue, 24 Mar 2026 14:05:09 +0800 From: Kairui Song To: Barry Song <21cnbao@gmail.com> Cc: kasong@tencent.com, linux-mm@kvack.org, Andrew Morton , Axel Rasmussen , Yuanchu Xie , Wei Xu , Johannes Weiner , David Hildenbrand , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , David Stevens , Chen Ridong , Leno Hou , Yafang Shao , Yu Zhao , Zicheng Wang , Kalesh Singh , Suren Baghdasaryan , Chris Li , Vernon Yang , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/8] mm/mglru: relocate the LRU scan batch limit to callers Message-ID: References: <20260318-mglru-reclaim-v1-0-2c46f9eb0508@tencent.com> <20260318-mglru-reclaim-v1-2-2c46f9eb0508@tencent.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Sun, Mar 22, 2026 at 04:14:31PM +0800, Barry Song wrote: > On Wed, Mar 18, 2026 at 3:11 AM Kairui Song via B4 Relay > wrote: > > > > From: Kairui Song > > > > Same as active / inactive LRU, MGLRU isolates and scans folios in > > batches. The batch split is done hidden deep in the helper, which > > makes the code harder to follow. The helper's arguments are also > > confusing since callers usually request more folios than the batch > > size, so the helper almost never processes the full requested amount. > > > > Move the batch splitting into the top loop to make it cleaner, there > > should be no behavior change. > > > > Signed-off-by: Kairui Song > > --- > > mm/vmscan.c | 19 +++++++++++-------- > > 1 file changed, 11 insertions(+), 8 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index d7fc7f1fe06d..d48074f9bd87 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -4689,10 +4689,10 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, > > int scanned = 0; > > int isolated = 0; > > int skipped = 0; > > - int scan_batch = min(nr_to_scan, MAX_LRU_BATCH); > > - int remaining = scan_batch; > > + unsigned long remaining = nr_to_scan; > > struct lru_gen_folio *lrugen = &lruvec->lrugen; > > > > + VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH); > > VM_WARN_ON_ONCE(!list_empty(list)); > > > > if (get_nr_gens(lruvec, type) == MIN_NR_GENS) > > @@ -4745,7 +4745,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, > > mod_lruvec_state(lruvec, item, isolated); > > mod_lruvec_state(lruvec, PGREFILL, sorted); > > mod_lruvec_state(lruvec, PGSCAN_ANON + type, isolated); > > - trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, scan_batch, > > + trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, > > scanned, skipped, isolated, > > type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON); > > if (type == LRU_GEN_FILE) > > @@ -4827,7 +4827,8 @@ static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec, > > > > *type_scanned = type; > > > > - scanned = scan_folios(nr_to_scan, lruvec, sc, type, tier, list); > > + scanned = scan_folios(nr_to_scan, lruvec, sc, > > + type, tier, list); > > Do we need to change this? That's a irrelevant blank line change, will drop it, thanks! > > > if (scanned) > > return scanned; > > > > @@ -4999,7 +5000,7 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc) > > > > static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > > { > > - long nr_to_scan; > > + long nr_batch, nr_to_scan; > > unsigned long scanned = 0; > > int swappiness = get_swappiness(lruvec, sc); > > > > @@ -5010,7 +5011,8 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > > if (nr_to_scan <= 0) > > break; > > > > - delta = evict_folios(nr_to_scan, lruvec, sc, swappiness); > > + nr_batch = min(nr_to_scan, MAX_LRU_BATCH); > > I wonder if we should modify get_nr_to_scan() to return > a maximum of MAX_LRU_BATCH？ We'll change that in a later commit to let each iteration use a smaller batch.