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b=Sin/qmdAh+e/cLQeAo844HNn73cnfzU0zCaK+3+yI6EQKZy9MgUHlMZfTkACMkyKc nGe+r3tk5rmd59+6VDMakoi4yvDy+lCSprKwKB40jG2KH9tw6FMzpGj8zK8RMSd6tl ucJ6SJywQ+x84Ds8R2AISvdvGCQ1omneuwqbqMFmEX9c+tygyAi+oSLR7Ceh8EoZdY RwXUqrzDidOWGTZvYHsTOClFSvEUF3qEY7oJX4970UNlbPwlbl6cC/MK2XbXWitZmS MZ+H7nmL51/ciAm6uORvQI3b6uzzQpDRPVn+eDRn1Q4SGg0TfFOSFYgy3zhSDsU/bi xcV5fhyeMurXQ== Date: Fri, 6 Mar 2026 17:44:04 +0200 From: Mike Rapoport To: Pratyush Yadav Cc: Pasha Tatashin , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] mm: memfd_luo: always make all folios uptodate Message-ID: References: <20260223173931.2221759-1-pratyush@kernel.org> <20260223173931.2221759-2-pratyush@kernel.org> <2vxzqzpybqyd.fsf@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2vxzqzpybqyd.fsf@kernel.org> X-Stat-Signature: whbm9nnosnyumobw8r9sh8q8k7h7f4ke X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: DF50540003 X-HE-Tag: 1772811851-994266 X-HE-Meta: U2FsdGVkX18yiDcEOYgV+NPkFPkA458zHlpCmnlVmWaDUsCgcyWuHhTKIIgl5StVvGRyWOivrFYOC7Ks6j573uBOtKIiDh3EAyk76S306/jl2c95ojdpAmb5NFYSyeTSZ68W26IPxScqzBNQvXZbUyJa8mC3mHZZed61GxDdnLnriQLdQ9wZD3Y34xXJq2beHdkrZCvUQtYMotWao4Wr2WpcKHXtHFd2NjL+DipdAOvrVreSn35vHY/LrlUoEuC3MNP2cmNE+lw9tGFTnvLeXF9g7xOOJwDg863iOebuBHZkjMUi/PP+RKv++wskELDtPN6wrDmEUll8vXnkoyDsZl/Ou0fxHVxQ58C0y3vHer1zGyW73S5nfJIcgTQQQRT8S4pKqzYVsi0cQTFD56vypdjt3pbD596Zwb5+WFN6XW+m9gIkk8YDpsnDLxIj7l1c8b+f/1EDkz0hCZgGZ3eZAnjzBW/+APNDApr3CnRWD5PHzCfrfFMK7Z8ngJjt5ypgS2aP6AgJ9XTlVytbVbGDPj+q8AobBafi3X6JnbN+hVsPvVvPkWdMlQghulxKjM3C9lWpj00lMreEGGHSrcMtUuJisiZo4tZ5XNE6DV0qVon9GDN48eDZX9NSBpVhr0JytaEN9CD9f0IP8OEJ3MLnpPf5kVFjDY1ydqP729esxGyQqhOO1uV/TLYSmVubYFKqrJuRcZ6fyuB7jGgSM+DctYRd1IdwK6g9XpLC83bYTG9xBwwjtIRUvWv34mAh+93caT2EYfk1ArMtzIJkSJkh3DjIBfUwzpbnxl2nuMsrmRpnXeQhkcqFGBQf1OxNtB4r/l0jX+/4Ily6ozsV0Cb8OMPi3HWphdFjICrTCuxs8mjvvhGAkE9aT5sCbCq86ZJhnCmWBXqhJkoTUCzY+ahoOXbQH/hweIZy/U/MxRKuJJmy23C2wO3TPodz7pMM2vKdJKtlWnaL8qulHedm//V ZrsLGfC9 2rN9Xetgei0YEH9yh0vpl4GUfm+bnmw3Xym+eQzxGqmXUUYrU403loJ0z2whIGpdyNnQqorDn5DQp3P87bRuSxq7S5VfFQ/KeCU9CNF6BpQTtTM7hsBOMFT9W0c7TiezCRtzBTV5iEU4DySOtDb0JBWCzLlv52RH/scdp1KaZ0Y3OdSGjYhVMWibCgFbXe080XsHv4p5ETVfDMg3uvGn948QM5wJwT5LVqcNXTOj+RQA0uLrDLsusY4hrnQ5gPIZfJJxrSMs5LH1muECmyOCpbimbBL2vhBLq2hBNAfwPE2fe5I4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Mar 05, 2026 at 09:50:18AM +0100, Pratyush Yadav wrote: > On Wed, Feb 25 2026, Mike Rapoport wrote: > > > On Mon, Feb 23, 2026 at 06:39:28PM +0100, Pratyush Yadav wrote: > [...] > >> + > >> + /* > >> + * If the folio is not uptodate, it was fallocated but never > >> + * used. Saving this flag at prepare() doesn't work since it > >> + * might change later when someone uses the folio. > >> + * > >> + * Since we have taken the performance penalty of allocating, > >> + * zeroing, and pinning all the folios in the holes, take a bit > >> + * more and zero all non-uptodate folios too. > >> + * > >> + * NOTE: For someone looking to improve preserve performance, > >> + * this is a good place to look. > > > > I'd add a larger comment above memfd_luo_preserve_folios() that says that > > it allocates, pins etc and fold the last two paragraphs of this comment > > there. > > How about this: > > /* > * If the folio is not uptodate, it was fallocated but never > * used. Saving this flag at prepare() doesn't work since it > * might change later when the folio is used. Make it uptodate > * now to avoid this problem. > */ > if (!folio_test_uptodate(folio)) { > > And the comment above memfd_pin_folios() gets this: > > * NOTE: For someone looking to improve preserve performance, this is a > * good place to look. Also look at the folio zeroing below. Looks great to me > [...] > > -- > Regards, > Pratyush Yadav -- Sincerely yours, Mike.