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Mon, 3 Apr 2023 14:22:41 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id nFUjHTHhKmRzFQAAMHmgww (envelope-from ); Mon, 03 Apr 2023 14:22:41 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id EF44AA0723; Mon, 3 Apr 2023 16:22:40 +0200 (CEST) Date: Mon, 3 Apr 2023 16:22:40 +0200 From: Jan Kara To: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net, ntfs3@lists.linux.dev, ocfs2-devel@oss.oracle.com, devel@lists.orangefs.org, reiserfs-devel@vger.kernel.org, Evgeniy Dushistov Subject: Re: RFC: Filesystem metadata in HIGHMEM Message-ID: <20230403142240.ftkywr3vn3r73yva@quack3> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: D691940002 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: cxf1nt3pbfmzr13fqy8pajpdpxe9195g X-HE-Tag: 1680531762-775632 X-HE-Meta: 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 yhOep55J DYjaiB2/GUMIrX7np0s+I2z1o8IIILpymo+ZCjNqFzHRSR9gbbd3roeOc70edSM5dqx9ihHNq+cAkVN+hDL3UugZHVppSKpdOJEIK2TaUdKSPAahDO8xUkyDq0rmGztPc5VqX30oIjygkrV+bZhzEe1vTh9tacDY/8Om0d77L9HOM89JFnJUKBU42Y2oOqFJ/7WqJRHQyuHS2nOWSkZ52k6PYliptVbfX2PwMUE1SSKybTR4= 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: On Tue 14-03-23 14:51:03, Matthew Wilcox wrote: > TLDR: I think we should rip out support for fs metadata in highmem > > We want to support filesystems on devices with LBA size > PAGE_SIZE. > That's subtly different and slightly harder than fsblk size > PAGE_SIZE. > We can use large folios to read the blocks into, but reading/writing > the data in those folios is harder if it's in highmem. The kmap family > of functions can only map a single page at a time (and changing that > is hard). We could vmap, but that's slow and can't be used from atomic > context. Working a single page at a time can be tricky (eg consider an > ext2 directory entry that spans a page boundary). > > Many filesystems do not support having their metadata in highmem. > ext4 doesn't. xfs doesn't. f2fs doesn't. afs, ceph, ext2, hfs, > minix, nfs, nilfs2, ntfs, ntfs3, ocfs2, orangefs, qnx6, reiserfs, sysv > and ufs do. > > Originally, ext2 directories in the page cache were done by Al Viro > in 2001. At that time, the important use-case was machines with tens of > gigabytes of highmem and ~800MB of lowmem. Since then, the x86 systems > have gone to 64-bit and the only real uses for highmem are cheap systems > with ~8GB of memory total and 2-4GB of lowmem. These systems really > don't need to keep directories in highmem; using highmem for file & > anon memory is enough to keep the system in balance. > > So let's just rip out the ability to keep directories (and other fs > metadata) in highmem. Many filesystems already don't support this, > and it makes supporting LBA size > PAGE_SIZE hard. > > I'll turn this into an LSFMM topic if we don't reach resolution on the > mailing list, but I'm optimistic that everybody will just agree with > me ;-) FWIW I won't object for the local filesystems I know about ;). But you mention some networking filesystems above like NFS, AFS, orangefs - how are they related to the LBA size problem you mention and what exactly you want to get rid of there? FWIW I can imagine some 32-bit system (possibly diskless) that uses NFS and that would benefit in caching stuff in highmem... Honza -- Jan Kara SUSE Labs, CR