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smtp.kernel.org (Postfix) with ESMTPSA id 00B51C4CEDD; Tue, 14 Jan 2025 15:49:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736869796; bh=pV3TS1U/Lbok5qyY+131cIEBJ5mcr+h9nvuWp50uRs4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=YxYCAFyCC4pP7lkMbYhT6e/Zf+Ch3kCCrcl7zzQ0VU0HyXQSHfrD1Md1RQkajePPI /+OUgQewvmBnn4d0afzj9LUdUwUFZxnxT2E2dhn4Rt4q7PKrN2hWQJIm8KajUE1/Ev U+/hEoiZN+Ou9oy4ELDQs5OAXRZqIeeG1rHDDiUddUe0/3OQhOn56JzCMA0Vrz6EyS JmLUm6ll6Z78qGex94LpVL6KkeWFPSyJhmL/N4c3qG/WBtONba7rvV3fr+fXIi2IE/ Rq19fGWnsiFZ+pMb4YKUVnI7FVNrNurP07xnkPv1WkKq9UwpROp37/CbcXyp6BxQ2e 1aq7pHtd/C3vw== Message-ID: <3c09175916c2a56b55d9cf61e4d8c0ea66156da2.camel@kernel.org> Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings From: Jeff Layton To: Miklos Szeredi Cc: David Hildenbrand , Shakeel Butt , Joanne Koong , Bernd Schubert , Zi Yan , linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko Date: Tue, 14 Jan 2025 10:49:54 -0500 In-Reply-To: References: <791d4056-cac1-4477-a8e3-3a2392ed34db@redhat.com> <1fdc9d50-584c-45f4-9acd-3041d0b4b804@redhat.com> <54ebdef4205781d3351e4a38e5551046482dbba0.camel@kernel.org> <2848b566-3cae-4e89-916c-241508054402@redhat.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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 fdaifG7u rb068LXHGHZBYAUfh7FfJ2A1Czpsf0MM3xt49bH5iLN6JPngVCShD9Pt1Vbb1sMPytEFc6dtpReCaTf+vchcv1NMDTpsVF5lzT7EA8oSeWhnapBZ4Um22/9BTkeafVDZvDkkC1+iRLdBDoKfRouwyOsjCQrxpyBMuh3w2ZjSW9xLBUzliWhb0jMLChd18U4bRf6RXC+vL6fs36diqizFSU6KT+QOhCWN1GI+lJSCxNmIlCfjCHeChqpx0r2bd7tDEW9FiCkCE+voOVmmDCsUho0HGlbYfJngCHfD2 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 Tue, 2025-01-14 at 10:40 +0100, Miklos Szeredi wrote: > On Tue, 14 Jan 2025 at 09:38, Miklos Szeredi wrote: >=20 > > Maybe an explicit callback from the migration code to the filesystem > > would work. I.e. move the complexity of dealing with migration for > > problematic filesystems (netfs/fuse) to the filesystem itself. I'm > > not sure how this would actually look, as I'm unfamiliar with the > > details of page migration, but I guess it shouldn't be too difficult > > to implement for fuse at least. >=20 > Thinking a bit... >=20 > 1) reading pages >=20 > Pages are allocated (PG_locked set, PG_uptodate cleared) and passed to > ->readpages(), which may make the pages uptodate asynchronously. If a > page is unlocked but not set uptodate, then caller is supposed to > retry the reading, at least that's how I interpret > filemap_get_pages(). This means that it's fine to migrate the page > before it's actually filled with data, since the caller will retry. >=20 > It also means that it would be sufficient to allocate the page itself > just before filling it in, if there was a mechanism to keep track of > these "not yet filled" pages. But that probably off topic. >=20 Sounds plausible. > 2) writing pages >=20 > When the page isn't actually being copied, the writeback could be > cancelled and the page redirtied. At which point it's fine to migrate > it. The problem is with pages that are spliced from /dev/fuse and > control over when it's being accessed is lost. Note: this is not > actually done right now on cached pages, since writeback always copies > to temp pages. So we can continue to do that when doing a splice and > not risk any performance regressions. >=20 Can we just cancel and redirty the page like that when doing a WB_SYNC_ALL flush? I think we'd need to ensure that it gets a new writeback attempt as soon as the migration is done if that's in progress, no? --=20 Jeff Layton