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[36.232.198.121]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a02738654csm2153372a91.3.2026.09.19.04.18.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 04:18:57 -0700 (PDT) From: Yuan-Hao Hsu To: David Hildenbrand 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 Subject: Re: [PATCH v2 2/2] mm/memory: reuse the whole exclusive large folio on a write fault Date: Sat, 19 Sep 2026 19:18:51 +0800 Message-ID: <20260919111851.678-1-aa9736195201@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <0c0c19d0-997a-4c8d-a103-2b3d153f4e32@kernel.org> References: <0c0c19d0-997a-4c8d-a103-2b3d153f4e32@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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.