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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 1431B180006 X-Stat-Signature: 3der8mj4j8sram7qdqfkd6yo7zustr68 X-Rspam-User: X-HE-Tag: 1789816738-359903 X-HE-Meta: U2FsdGVkX19B6LMa8WZUKHR6qcp8AwOW9DVeX5nLPBL2IPSZ1RucTlCXuqGfJKOlHZPQld3l7S8KHq4Iy8e16z5am5C+xnlXcoU+kDsY4wORdOyEs2M1Lx0xUFXXxeu0f3mid94BwbJS/6m5yVljFM8C7bHzhuC/o182Myf4kNeVFnkKla/0YrCAeSnrL+VMQStwvR1c5ewuGybLYwR/7rpJcCAJMnpeb5a+aEbY3/as/LKCdQengh3jAdTkMxEfWhfh/9TwRkxRsnZiJ9erZhC4YhEOWxq7aDo83O0ExrxPkOKyYD+gY4BNNJFmUH+PwwI/M2Fo4pDJGrPymX2+GThdn2U7Q2xPXKiwtGFuO+7LwOIAKJJvvXJ7dasVlg8Po+XGc6e+CZefPYy7N100o6znlsW52o1MgvCg8TzfOrWD6pdu6AeNVoMFWF1SZZazdgOVt9p5Z+K4G6N4TgKh692XxU8O9R/BdFq1nXHlDYUfZvZ4RRKKOwJoLxXdkAGMjiLM2tNoN2yrNeWvl8y/KVp5nUMnH2GhdTw+8cNkyiFxI6BNxKQnk6v82IgRnY8ehnTY16lSgiWB6YDNmGB9/DN11d9aY8D1WMJShYduebRY7wpjuxo0rntOGOc3ts5f51jatc+4npUCQgh4Fjh1yGnOzxDpgykqxjFGoFysyUKkHst3QU7gwfa4etmAYSVooHFUVJi1qzoea4RrsRyAK4N74t/B5JVLV9Urxm108mnWwfrfQxpyuphww5rF8jzvqsaHKiSNbglDO2EfDRPj7y2Uq/d7/4vLxk13NDlsxJDn1blIf3V97zHB+hKqFQ4SHbIMzYYOBXE+/RRpyKcCRuFm87mnu+kXh/xsr5T6pt3W2O0IMpjtHEV6GlIn+IYI6Yf/wbDaTFt1xmKb/UuaysugjUz6mwNa0P9gKJuhueh6QPzNUX3yVr37uVoVZFH23mjHaRRwdeLNz1OWDKb W2zioL85 RQJWz4Cd1HRWmI/zDGgW6wbt6EQN/Wb8MansMwvy/vdU/v2qQrqgE7eME+gB6JPyb+/sOueBVCgWEPqxfjeVrHbhIf3KqHHU3PhtAig3i3nQvDuhMupemYNLa6/DYrQ984EWf4yU38ItYNVYa8TiMpJe0ZOeYTk3qZaSlMM5u9Jma5W/8ZpzmjMTAzzknYkXGytvIEGz500rtyB19hSKexpQ11ePyLajeeJd5sf8dcOMFxFU9h70XHjNKAQ6+hKvGtJNOS+BBzpbPDzVqINXSs/kyLbX2qB0ucKVqoTPMq4O2TLc6NuKF+pMiB4yDvePeypffFCZoi5jmEua2jmfGfwdom/73xSe6EfuneForfECClNkgzgp3qP2xxGVWbH4rFnkY Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.