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b=pR+/MY0Qaw1o61uWOSxUf1fOTO rVCl2RdEbFl5fqSjcqYn0uYhBgBMMOQrSZdd1WEcikQcpc4m21mUTaoEXhTrHGm+mSSLaPWip44dt FzDoES5HUEHizaSBHcqZBXN/ghiiH+YPnRgmm41Xvx/srSa1r+od8ux1+ku/DeboOgbkBX0fk2877 wAZuPLFEBq2RQpIDBBexqUh8x0hSU2iyL3jqt4Gyfg7VGrWlAncEw98XGrw94y0sXrOFvM+tvBFQH qbE71HhdMq4bJc9YSbEpoCbpKb+MvPQ5UvfP3TeHxBfy09zEoaKS80ozzt0TZ2vUCn5bQQwxpxm86 kGRhyNTg==; Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vL8YW-0000000EZso-3OIP; Mon, 17 Nov 2025 23:22:44 +0000 Date: Mon, 17 Nov 2025 23:22:44 +0000 From: Matthew Wilcox To: Ackerley Tng Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@redhat.com, michael.roth@amd.com, vannapurve@google.com Subject: Re: [RFC PATCH 0/4] Extend xas_split* to support splitting arbitrarily large entries Message-ID: References: <20251117224701.1279139-1-ackerleytng@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251117224701.1279139-1-ackerleytng@google.com> X-Rspamd-Queue-Id: 44EA31C0007 X-Rspamd-Server: rspam07 X-Stat-Signature: huk51iddiquc7x77d6te5q6p13ffkuob X-Rspam-User: X-HE-Tag: 1763421768-211051 X-HE-Meta: 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 c7ByJQgY PicUUOF/tRZRENkC6c8g8YIE/uold7DuldRXpRkzUsyyvdGYUFGpc2v//yF/Ni0zkZHqpcYQn1bzNZYdxnBl61h6pHOFpK31sGj+UZ9mdr38F4a8Y7Hnva1kLx7g+bSb4fiWcFhOV6if5gSLzhVKzmNKzEdLHxwjSxdixzi2x8Gb3A7Arseh8mBTG6bMFKeugaGZkHmkpFWWC8czcZAueWBtHcMVjU4ED69mMV/IYrfpnqmMxTR/nVMkiDgy5/cN6Dy2o+HQ6n+wD8HC4iAAoI/TzWNzm++W9ePEq5dBCRIhsglc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Mon, Nov 17, 2025 at 02:46:57PM -0800, Ackerley Tng wrote: > guest_memfd is planning to store huge pages in the filemap, and > guest_memfd's use of huge pages involves splitting of huge pages into > individual pages. Splitting of huge pages also involves splitting of > the filemap entries for the pages being split. Hm, I'm not most concerned about the number of nodes you're allocating. I'm most concerned that, once we have memdescs, splitting a 1GB page into 512 * 512 4kB pages is going to involve allocating about 20MB of memory (80 bytes * 512 * 512). Is this necessary to do all at once?