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b=AyfLcPLrRvfchnBfMKPYwdOOu1UiM4BKHqjiErohamcPpOdn65yzlIGyPrwF0e7px 83dSOl3MRI8wwykW/cJ0Vv/TA2kldAaYueeVhCq4+NpEAbNja3fMIJyUYR0ilM0GWk Pjxb8MsZdOLyEIaxn02C80FNsR72mymDBLdruRJs= Date: Wed, 17 Dec 2025 10:54:26 -0800 From: Andrew Morton To: Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, david@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, mjguzik@gmail.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, willy@infradead.org, raghavendra.kt@amd.com, chleroy@kernel.org, ioworker0@gmail.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH v10 7/8] mm, folio_zero_user: support clearing page ranges Message-Id: <20251217105426.5f03b5e8abd2e50faee9f49f@linux-foundation.org> In-Reply-To: <87fr994hot.fsf@oracle.com> References: <20251215204922.475324-1-ankur.a.arora@oracle.com> <20251215204922.475324-8-ankur.a.arora@oracle.com> <20251215184413.19589400a74c2aadb42a2eca@linux-foundation.org> <874ipqexai.fsf@oracle.com> <20251216071250.e49ecf7490acf7f377dbfdc0@linux-foundation.org> <87fr994hot.fsf@oracle.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 23E16140010 X-Stat-Signature: sj96jpar6uxrijq76umzo4epihh3kcaa X-Rspam-User: X-HE-Tag: 1765997669-680183 X-HE-Meta: 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 cYiakJqq qHoGTE32h9f3BZYCE8rFzemo5Af3TrNW+Vhqm6CfoQsicxtLmCLcp0Sbm6uw1WACKBWx6mwcgYlZqsMJOv7P9rEukI56c3rIq4iJpVsxR2clg1Kw8ydQYiobApXzFtapebeJaJQk6ocC5z7ubRvlTZPXaqn2k7/8CI8DpBskMcqM892Q0+JX8u8GnnbBZa8C0jzyAnvsUF/Kr9uxY5UPGLhT8lfaqvRHqVxlrYozzVKmed7uB053F4mPrddt08IcUz9Eha6esj5Vypxy8wsKXBEhgX++OtgQ6Cwu46GC9QmgbRJ7TQd1dZKkbSLpDNjPoqB1K 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: On Wed, 17 Dec 2025 00:48:50 -0800 Ankur Arora wrote: > > At 42GB/sec, 32MB will take less than a > > millisecond, yes? I'm not aware of us really having any latency > > targets in these preemption modes, but 1 millisecond sounds pretty > > good. > > Agreed. The only complaint threshold I see is 100ms (default value of > sysctl_resched_latency_warn_ms) which is pretty far from ~1ms. > > And having a threshold of 32MB might benefit other applications since > we won't be discarding their cachelines in favour of filling up the > cache with zeroes. > > I think the only problem cases might be slow uarchs and workloads where > the memory bus is saturated which might dilate the preemption latency. > > And, even if the operation takes say ~20ms, that should still leave us > with a reasonably large margin. > (And, any latency senstive users are probably not running with > preempt=none/voluntary.) So I think you're saying that yes, we should increase the chunk size? If so, what's the timing on that? It would be nice to do it in the current -rc cycle for testing reasons and so the changelogs can be updated to reflect the altered performance numbers.