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b=Bw38b5kfGJ8hqmEOgHH5FNV548X9MkggalAx/zMvWpGcRMxJXJS+4pY+NUARg01n7 +cNe5svEU3+SAubK2jGKIc7Me7FJD2vjPl9yhIJaD9RUVCcDMvKKlpb6RQfiXDdC6y hLI3tSr/Pv2BUlcgxas/bWu7AzTABrzdeHsliiiU= Date: Sun, 5 Jul 2026 01:00:00 -0700 From: Andrew Morton To: Cc: , , , , , , Subject: Re: [PATCH v11 =?UTF-8?B?MC8zXcKgS1NNOg==?= performance optimizations for rmap_walk_ksm Message-Id: <20260705010000.1f9b63735aa19fbfb5d9c24f@linux-foundation.org> In-Reply-To: <20260703162253688u8Str9eFLR8TGCmo7nIOF@zte.com.cn> References: <20260703162253688u8Str9eFLR8TGCmo7nIOF@zte.com.cn> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 71EB6180006 X-Stat-Signature: c5fkzwye69hrg85cmtq1nigkoqhx8if8 X-Rspam-User: X-HE-Tag: 1783238402-366061 X-HE-Meta: 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 Yg47UdDR 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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 Fri, 3 Jul 2026 16:22:53 +0800 (CST) wrote: > This series fixes a severe KSM reverse-mapping performance problem > that can freeze applications for hundreds of milliseconds under > memory pressure especially when a lot of unrelated VMAs sharing a > single anon_vma. > > Two key highlights: > > 1. Lock hold time drops from >500ms to <2ms > - In our benchmark (20,000 VMAs sharing an anon_vma), worst-case > anon_vma lock hold time during KSM rmap walk went from 705ms > down to 1.67ms (max) and 1.44ms (avg). > > 2. Real user impact > - The anon_vma lock is also acquired by page faults, reclaim, > migration, compaction, mlock, exit_mmap, and cgroup accounting. > > - A long hold due to inefficient rmap walks stalls application > threads, causing latency spikes, reduced throughput, or even > container timeouts. > > - The problem occurs even without fork() – VMA splitting (e.g., > via mprotect or madvise over time) can create tens of thousands > of VMAs all attached to the same anon_vma. > > Real-world examples: Again, thanks for persisting with this. Great improvement and I'd love to see us get this finished off. Please have a look through the AI review: https://sashiko.dev/#/patchset/20260703162253688u8Str9eFLR8TGCmo7nIOF@zte.com.cn That 32-bit thing looks legit, kinda fatal but easy to address.