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by smtp.kernel.org (Postfix) with ESMTPSA id 0A16EC4CEDD; Tue, 14 Jan 2025 15:44:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736869461; bh=jTzvlPGpoCX9x9yCpHaLfBghwnzXHznfP6+iD76KWfk=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=or9Q8HrdM9uLRTE7AUDTVpdkxMEFuj7D+k7A1MkDXfRtwU+2Si158UukVItkDkask JEUyuyPQusCmwFoZJpM0/PMqWQGtL17Iv5lq5IV7L56mcu6kJijBGT7gHTUroq8M3E flrI5rPCc3dt9EyrE8J+W0fJ/dKZMihM4+Sc81lfpx4E5oTDug1B11mgFVrOWk/EGm NZzaeugTEmH/VSEpN3xnL+OT/Ne4zwUp5nbwkrwPJgXG0GoXuRYXr6bETmMRYXzlz5 koM2kDpgGMIy3pFb5IT8rNzJLLANrzdCYkGhc/ban+FkDraEwKEkwTwKtH5spHHPUN EaFZdtTrwQ95w== Message-ID: 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 10:44:18 -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 VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ 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 y1rwqgDj /HrxW2qDneBlxwhP8JHpYa+laB45ws8fjC82ErZopBAF0/T5SphVSnK+erGnk9qib3h7az+LYL/EycwkEimg7+wZB30+4d5q1p804Wnc2JSE12gHAsCBLIpn1w8xzTDbYJXnJodlYKgOqqhh2r0Y/pnC5yq+ZxKgod+yo5u59RDFehDE3bTsnHRNripzKt1D5o2Cvx1KK5FV4sTUCb+9+eU6zJjS/iXnoly/fwcHQ74HSFSCJsOQVkDO9RrH5pFMHnjYeXaAEzFjRmKQgtpM/0y9xFNsAFogzugd1drZn8ZGT874= 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 09:38 +0100, Miklos Szeredi wrote: > On Mon, 13 Jan 2025 at 22:44, Jeff Layton wrote: >=20 > > What if we were to allow the kernel to kill off an unprivileged FUSE > > server that was "misbehaving" [1], clean any dirty pagecache pages that > > it has, and set writeback errors on the corresponding FUSE inodes [2]? > > We'd still need a rather long timeout (on the order of at least a > > minute or so, by default). >=20 > How would this be different from Joanne's current request timeout patch? >=20 When the timeout pops with Joanne's set, the pages still remain dirty (IIUC). The idea here would be that after a call times out and we've decided the server is "misbehaving", we'd want to clean the pages and mark the inode with a writeback error. That frees up the page to be migrated, but a later msync or fsync should return an error. This is the standard behavior for writeback errors on filesystems. > I think it makes sense, but it *has* to be opt in, for the same reason > that NFS soft timeout is opt in, so it can't really solve the page > migration issue generally. >=20 Does it really need to be though? We're talking unprivileged mounts here. Imposing a hard timeout on reads or writes as a mechanism to limit resource consumption by an unprivileged user seems like a reasonable thing to do. Writeback errors suck, but what other recourse do we have in this situation? We could also consider only enforcing this when memory gets low, or a migration has failed. > Also page reading has exactly the same issues, so fixing writeback is > not enough. >=20 Reads are synchronous, so we could just return an error directly on those. > 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 We already have a ->migrate_folio operation. Maybe we could consider pushing down the PG_writeback check into the ->migrate_folio ops? As an initial step, we could just make them all return -EBUSY, and then allow some (like FUSE) to handle the situation properly. --=20 Jeff Layton