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AJvYcCWQ284C3jd4Kb4q5VHYbTbJYaRXSxg74cdfePxtmMyUI9RWFxUFOsi3+apqmjwqWPuOE5+5eWAdjw==@kvack.org X-Gm-Message-State: AOJu0YyiFohZj4smBi1qXsW9dVxuwtF46ybYjqsyWeKisofwptBGBmSi 4iSOh63dWZ5doHbN7PYqsw8pDPzJ33TKrDZSol8pnat9KVjuhjBqSbAAIbgKw/e6ioRF4G59A/L UK/UVwjNFlVWG1ITj2O+E+9B5QSc= X-Gm-Gg: ASbGncvzzdYsqP44qL8TxMjKwIZ0kHTg3FJuM/c6IxUmzeiJhfvqh1kXCtPLCpHPbVl oQiDERDB3Bw4DBDxKsX2WAZFzRkVMxstxoA0bZOFrOOAxm7AaDZH6dFLVjGC8OEQHUrzAdP/r X-Google-Smtp-Source: AGHT+IGECQ/w8NYEYhSTYaIQyLcN66M2+51+04/4AOe2T1wrymBLUIuUHxCONze2paBjPVSYAhXEOCKf4kAD5CasAtA= X-Received: by 2002:a05:6102:440b:b0:4af:aaa4:dd9a with SMTP id ada2fe7eead31-4b2477b6361mr2762431137.10.1733993696435; Thu, 12 Dec 2024 00:54:56 -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 21:54:45 +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-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D7E92140008 X-Stat-Signature: p7rybannnauro3r1dzeth73ryebxnqif X-Rspam-User: X-HE-Tag: 1733993680-668355 X-HE-Meta: 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 S+T6fk9T 2Cj7vZvWO618N6yMq1FRBrlkOPPWc+Yy1cjT6i0GqUQXfXGZGHGpfs3yhQsYNMZOcT5AYlB1td3nbTwwNZQyBgobLlkuMa+wYJ6H9VtCv5hQ0dGRrFzZ7MfwvNpUR6WKij45Qp98hEK31YitGRID/XR8E1AkWEtoHECTVwRBDOoqv0WDVBRYxh8WmUXvcQVrY3c1cjXrZFzBYXa9MzdiwZh8ty5B6ZE5/9QnBTTLZvZm0DSER0EUGMk6VZQWDISRi37bzLT8R8UjQls+T6L4pdJHsY+SPFIletLUhf+NHtkYjC+7BJFGU7NfJaEpxMGG8xsuGB7ra92/e35dAXGbrChTNezjxr4HIeJAf+wTlk/Wf7tF6RHt1EpZRZPc/ccrelduw3H4NAIL16cmutf5gqprTiae6V7IB21SFxMLpkUnKCL8TFmM/9EiUrbNYH8nSodBmYApV4GrZ/38= X-Bogosity: Ham, tests=bogofilter, spamicity=0.242031, 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 9:50=E2=80=AFPM Christoph Hellwig wrote: > > On Thu, Dec 12, 2024 at 09:46:03PM +1300, Barry Song wrote: > > 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 li= ke you might > > not have fully read the code. :-) > > I've not read the code at all, I've read your commit log. > > > 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 = could > > save the memory used by this page. > > Yes. But why do that in swap-in and not swap-out? Usama implemented this in swap-out, where no I/O occurs after his zeromap series. A bit is set in the swap->zeromap bitmap if the swapped-out page is zero-filled. and all swapp-out I/O is skipped. Now, the situation is that when we re-access a swapped-out page, we don=E2=80=99t always need to allocate a new page. Instead, we can map it to zero_pfn and defer the allocation until the page is written. >