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From: David Sterba <dsterba@suse.cz>
To: David Howells <dhowells@redhat.com>
Cc: willy@infradead.org, hch@lst.de, trond.myklebust@primarydata.com,
	Theodore Ts'o <tytso@mit.edu>,
	linux-block@vger.kernel.org, ceph-devel@vger.kernel.org,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Jeff Layton <jlayton@kernel.org>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	linux-mm@kvack.org, Bob Liu <bob.liu@oracle.com>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Josef Bacik <josef@toxicpanda.com>,
	Seth Jennings <sjenning@linux.vnet.ibm.com>,
	Jens Axboe <axboe@kernel.dk>,
	linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-ext4@vger.kernel.org, linux-cifs@vger.kernel.org,
	Chris Mason <clm@fb.com>, David Sterba <dsterba@suse.com>,
	Minchan Kim <minchan@kernel.org>,
	Steve French <sfrench@samba.org>, NeilBrown <neilb@suse.de>,
	Dan Magenheimer <dan.magenheimer@oracle.com>,
	linux-nfs@vger.kernel.org, Ilya Dryomov <idryomov@gmail.com>,
	linux-btrfs@vger.kernel.org, viro@zeniv.linux.org.uk,
	torvalds@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH v3 0/9] mm: Use DIO for swap and fix NFS swapfiles
Date: Mon, 27 Sep 2021 22:07:08 +0200	[thread overview]
Message-ID: <20210927200708.GI9286@twin.jikos.cz> (raw)
In-Reply-To: <163250387273.2330363.13240781819520072222.stgit@warthog.procyon.org.uk>

On Fri, Sep 24, 2021 at 06:17:52PM +0100, David Howells wrote:
> 
> Hi Willy, Trond, Christoph,
> 
> Here's v3 of a change to make reads and writes from the swapfile use async
> DIO, adding a new ->swap_rw() address_space method, rather than readpage()
> or direct_IO(), as requested by Willy.  This allows NFS to bypass the write
> checks that prevent swapfiles from working, plus a bunch of other checks
> that may or may not be necessary.
> 
> Whilst trying to make this work, I found that NFS's support for swapfiles
> seems to have been non-functional since Aug 2019 (I think), so the first
> patch fixes that.  Question is: do we actually *want* to keep this
> functionality, given that it seems that no one's tested it with an upstream
> kernel in the last couple of years?
> 
> There are additional patches to get rid of noop_direct_IO and replace it
> with a feature bitmask, to make btrfs, ext4, xfs and raw blockdevs use the
> new ->swap_rw method and thence remove the direct BIO submission paths from
> swap.
> 
> I kept the IOCB_SWAP flag, using it to enable REQ_SWAP.  I'm not sure if
> that's necessary, but it seems accounting related.
> 
> The synchronous DIO I/O code on NFS, raw blockdev, ext4 swapfile and xfs
> swapfile all seem to work fine.  Btrfs refuses to swapon because the file
> might be CoW'd.  I've tried doing "chattr +C", but that didn't help.

There was probably some step missing. The file must not have holes, so
either do 'dd' to the right size or use fallocate (which is recommended
in manual page btrfs(5) SWAPFILE SUPPORT). There are some fstests
exercising swapfile (grep -l _format_swapfile tests/generic/*) so you
could try that without having to set up the swapfile manually.

  parent reply	other threads:[~2021-09-27 20:07 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-24 17:17 David Howells
2021-09-24 17:18 ` [PATCH v3 1/9] mm: Remove the callback func argument from __swap_writepage() David Howells
2021-09-24 17:18 ` [PATCH v3 2/9] mm: Add 'supports' field to the address_space_operations to list features David Howells
2021-09-24 20:10   ` Matthew Wilcox
2021-09-24 17:18 ` [PATCH v3 3/9] mm: Make swap_readpage() void David Howells
2021-09-24 22:07   ` Matthew Wilcox
2021-09-24 17:18 ` [PATCH v3 4/9] Introduce IOCB_SWAP kiocb flag to trigger REQ_SWAP David Howells
2021-09-26 21:56   ` Dave Chinner
2021-09-24 17:18 ` [PATCH v3 5/9] mm: Make swap_readpage() for SWP_FS_OPS use ->swap_rw() not ->readpage() David Howells
2021-09-24 17:18 ` [PATCH v3 6/9] mm: Make __swap_writepage() do async DIO if asked for it David Howells
2021-09-24 17:19 ` [PATCH v3 7/9] nfs: Fix write to swapfile failure due to generic_write_checks() David Howells
2021-09-24 17:19 ` [PATCH v3 8/9] block, btrfs, ext4, xfs: Implement swap_rw David Howells
2021-09-24 17:19 ` [PATCH v3 9/9] mm: Remove swap BIO paths and only use DIO paths David Howells
2021-09-25 14:56   ` Matthew Wilcox
2021-09-25 15:36   ` David Howells
2021-09-25 17:09     ` Matthew Wilcox
2021-09-26 23:08       ` Damien Le Moal
2021-09-27  1:25         ` Dave Chinner
2021-09-27  1:41           ` Damien Le Moal
2021-09-27 20:03     ` David Sterba
2021-09-25 23:42 ` [RFC][PATCH v3 0/9] mm: Use DIO for swap and fix NFS swapfiles Dave Chinner
2021-09-26  3:10   ` Matthew Wilcox
2021-09-26 22:36     ` Dave Chinner
2021-09-27 20:07 ` David Sterba [this message]
2021-09-28  3:11 ` NeilBrown
2021-09-30 15:54   ` Steve French
2021-09-30 15:54     ` Steve French
2021-09-29 15:45 ` David Howells

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