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Thu, 04 Dec 2025 01:05:47 -0800 (PST) From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, axelrasmussen@google.com, chenridong@huawei.com, chenridong@huaweicloud.com, hannes@cmpxchg.org, jaewon31.kim@samsung.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, lujialin4@huawei.com, mhocko@kernel.org, shakeel.butt@linux.dev, weixugc@google.com, yuanchu@google.com, yuzhao@google.com, zhengqi.arch@bytedance.com, Lance Yang Subject: Re: [PATCH -next] mm: vmscan: correct nr_requested tracing in Date: Thu, 4 Dec 2025 17:05:34 +0800 Message-ID: <20251204090534.22909-1-ioworker0@gmail.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <98cbf348-ff21-4c90-af32-b8009c34e5fd@kernel.org> References: <98cbf348-ff21-4c90-af32-b8009c34e5fd@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 66904100012 X-Stat-Signature: y57kxg7hn6j5cdr8b9joyknnhg7zegb6 X-Rspam-User: X-HE-Tag: 1764839149-839803 X-HE-Meta: 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 AR6TOQ9r d3VO7Veb/XDyw5TmtZHzNl+dYNnLQGSTcdQ7e5INBcSm4pxKOTvYr1rN3bim4ztbkm8tAT+bj7ejQHBbrNzV1WdHRZXb6Qx8p5yqZlGesl5EGVAQ= 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: From: Lance Yang On Wed, 3 Dec 2025 12:33:07 +0100, David Hildenbrand (Red Hat) wrote: > On 12/3/25 10:40, Chen Ridong wrote: > > From: Chen Ridong > > > > When enabling vmscan tracing, it is observed that nr_requested is always > > 4096, which is confusing. > > > > mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ... > > mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ... > > mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ... > > mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ... > > mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ... > > mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ... > > mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ... > > > > This is because it prints MAX_LRU_BATCH, which is meaningless as it's a > > constant. To fix this, modify it to print nr_to_scan as isolate_lru_folios > > does. > > > > Fixes: 8c2214fc9a47 ("mm: multi-gen LRU: reuse some legacy trace events") > > Signed-off-by: Chen Ridong > > --- > > mm/vmscan.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index fddd168a9737..8cfafd50a7a8 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -4601,7 +4601,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, > > count_memcg_events(memcg, item, isolated); > > count_memcg_events(memcg, PGREFILL, sorted); > > __count_vm_events(PGSCAN_ANON + type, isolated); > > - trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, MAX_LRU_BATCH, > > + trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, > > scanned, skipped, isolated, > > We do that in isolate_lru_folios(). > > Given that we do > > int remaining = min(nr_to_scan, MAX_LRU_BATCH); > > and effectively cap it, I wonder if we would want to trace that capped > valued instead of MAX_LRU_BATCH. Yeah, since we explicitly clamp the work at MAX_LRU_BATCH, the trace should reflect that reality :)