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AJvYcCW6CQpmDKvczby6Kyh/LbFKtR6WqkbiJ4SVjOu7SqFCgiU59nf5ZxKyAXEtbnVD5KKvREq6yL29Ug==@kvack.org X-Gm-Message-State: AOJu0YxnZMn7H8T8EW6UNeqEfsTxyguzBrEPVsiM7A+LE4Q3LUsaePWF 1Vy8wczEkbHuHfKXfep1RUirGVYrJo5zicFoiYzEwFAk7PmRYn+YxYlnIu0nJjY09/A5/WPvN/h zuj2ZQeQurgrW5BkfVNMi5iSEPGY= X-Gm-Gg: ASbGncu3IsdU4sP8V8NRxxy1rMdIJTaw+rflTZrlVOg7vInyyRWBWEj6L4G9MbBRKzQ I83xmnWDIkRIgRlG1C1kN2MjJQRsHK/ZSW1fEE0nRb8bJlfVlPsFuDbng6l7biZ4ZznQeuV2F X-Google-Smtp-Source: AGHT+IEoADavB1JIm+murNeLnxY5eMbts83wvxM3I3vkEtAkbjquGmP0H3dANejT607YVUwCOExNKVA1QJUpACXlzco= X-Received: by 2002:a05:6102:3746:b0:4af:ba27:72d6 with SMTP id ada2fe7eead31-4b2477e8dcamr2861269137.14.1733993174202; Thu, 12 Dec 2024 00:46:14 -0800 (PST) MIME-Version: 1.0 References: <20241212073711.82300-1-21cnbao@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Thu, 12 Dec 2024 21:46:03 +1300 Message-ID: Subject: Re: [PATCH RFC] mm: map zero-filled pages to zero_pfn while doing swap-in To: Christoph Hellwig Cc: akpm@linux-foundation.org, linux-mm@kvack.org, axboe@kernel.dk, bala.seshasayee@linux.intel.com, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, kanchana.p.sridhar@intel.com, kasong@tencent.com, nphamcs@gmail.com, ryan.roberts@arm.com, senozhatsky@chromium.org, terrelln@fb.com, usamaarif642@gmail.com, v-songbaohua@oppo.com, wajdi.k.feghali@intel.com, willy@infradead.org, ying.huang@linux.alibaba.com, yosryahmed@google.com, baolin.wang@linux.alibaba.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 9e3yedd147u9obfr781hpnoa38agdf9g X-Rspamd-Queue-Id: 368F480012 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1733993129-302409 X-HE-Meta: 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 8IZq82QX mwVASs1cjYrFZEVZ/DFOz2TP59qYxZHeAcYz6PLB93QpALXcaaw21WueZMXGmOi1e54tgB4G2cshdkUIz2KIwmaFt1Uv1zL7MKm7eqWzzUqA4YZYxivhU+7mltCGq4xd3+v0w+0WgQZ2CI9Rw4jmTN0mLASBdwj5CfcyVUqSvcBtii1qykfIuFQ0jhzwP+U1Tw4jWAdxmzHmA2/vF3j7GW4Ibz8adaA32X+HiYWXQiAh5f3f/h0YVpSf0vhYYIEuQbkhMhFynYiFHy0G0AV8UG0cZ3F8xa1OcrMMjtkHpMSovOFJ2OaHxMKY3Q4+c46C6lKus9y/dAlBfpzSaev+7wXTbN9EtujlZLxlllpklqTNhmR+NoW23M/BV2iKGgFI03lNchC3ATPgOl/Gt/iB69rdZfGTREBZwuNTIomrD4ioyLT7tA/sztNZDvF95vwUzpNzs X-Bogosity: Ham, tests=bogofilter, spamicity=0.426291, 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 Thu, Dec 12, 2024 at 9:29=E2=80=AFPM Christoph Hellwig wrote: > > On Thu, Dec 12, 2024 at 08:37:11PM +1300, Barry Song wrote: > > From: Barry Song > > > > While developing the zeromap series, Usama observed that certain > > workloads may contain over 10% zero-filled pages. This may present > > an opportunity to save memory by mapping zero-filled pages to zero_pfn > > in do_swap_page(). If a write occurs later, do_wp_page() can > > allocate a new page using the Copy-on-Write mechanism. > > Shouldn't this be done during, or rather instead of swap out instead? > Swapping all zero pages out just to optimize the in-memory > representation on seems rather backwards. I=E2=80=99m having trouble understanding your point=E2=80=94it seems like y= ou might not have fully read the code. :-) The situation is as follows: for a zero-filled page, we are currently allocating a new page unconditionally. By mapping this zero-filled page to zero_pfn, we coul= d save the memory used by this page. We don't need to allocate the memory until the page is written(which may ne= ver happen). > Thanks Barry