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b=Ue+9AbvBliMX+AIYWSvzQWUAHjFI3jdLOlYH/aiNY3rhxae13ZiGjmWsr8aJZNcpr MfQ1/lX8DbksvJiuh/nkNXdhKQe81Z2d8J4cm9YHvfu0c61XAOxufIl4bGlteKSYa8 3ZxGS5STiI1p6uzVLM6rQlB7RiVVJOjXfEvc4MfFDn0cZrc/5OGQij2Y5y8akxyKOt QrJ8ML2y4spobTgcJPcgtV+cNiAaLhG9i5cVWxzjvybQ87SHmd0fMDX5VkeYBwd8R7 VNVePZoQSbnizLpo3ctvplSR/tUOuDV4rK1BKVLcgMxf8plzTKyPdXN+oUImJ7G2wI SWj4KOKPH2BTQ== Message-ID: <25cae0dd-6b4b-4519-8119-231e2f65da46@kernel.org> Date: Thu, 24 Sep 2026 21:54:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/memory: reuse the whole exclusive large folio on a write fault To: Yuan-Hao Hsu Cc: Andrew Morton , Lorenzo Stoakes , liam@infradead.org, Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Barry Song , Ryan Roberts , Dev Jain , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <0c0c19d0-997a-4c8d-a103-2b3d153f4e32@kernel.org> <20260919111851.678-1-aa9736195201@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: boyrweasj4wpenoiewfbigxrpijm8cg7 X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9B7E01A0002 X-HE-Tag: 1790279655-603386 X-HE-Meta: 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 DNTKZhGR iieFiJf1hcA9/Sd6SNJXRcLwpZoqJv3O9RD863+nX3fpIjZePRpw84GlYYgUOccT9t64nrN2P8LSXelqQq9AxER+TNPuCHPxQ8ufXT6I7YyGIcYdJjt+eH0DO+WW+l+DR1FY9tXtlGmFrWNLYy3McLtuEHvoVR73gSEs8SsMFsgsu/4Vyj7RMxO+AnqiGgNl9Uxepkwu75EwdRGYoherAq/3i16pZei63SXWYBa+OcuYCp4LyQi2cjERO0rnbpY9oFy1vrEP0gqtkNDs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/19/26 13:18, Yuan-Hao Hsu wrote: > On Sat, 19 Sep 2026 12:10:56 +0200, David Hildenbrand (Arm) wrote: >> Are you measuring the worst-case latency of a single write fault or only the >> average over all writes? > > The single fault. Each store is timed by itself (clock_gettime() > before and after), and the latency numbers come from a pattern where > every store takes one of these faults (one store per folio), so there > is nothing else in the average. The tables show the median of those > faults; I also have p99 and max (i7-12700KF, in a VM, us): > > v7.3-rc3+ patched > p50 p99 max p50 p99 max > 64K, 1 fault 0.42 0.57 25-26 0.71-0.74 0.96-1.10 28-60 > 2M, 1 fault 0.50 0.67 0.7-1.2 10.0-10.2 12.2-15.8 13-22 > > max is the slowest store of a run, median over 15 runs. The 25 us on > the base kernel are interrupts; the VM has those on both sides. The > 2M row is the worst case by construction, every one of those faults > walks all 512 PTEs. Thanks. See my other mail, we should focus on keeping the fault path as fast as possible and minimizing the work in there. -- Cheers, David