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From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
	Mike Marshall <hubcap@omnibond.com>,
	Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-mm@kvack.org, linux-cachefs@redhat.com,
	linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org,
	linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
	v9fs-developer@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org, Jeff Layton <jlayton@redhat.com>,
	David Wysochanski <dwysocha@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 03/33] mm: Implement readahead_control pageset expansion
Date: Wed, 17 Feb 2021 22:49:18 +0000	[thread overview]
Message-ID: <20210217224918.GP2858050@casper.infradead.org> (raw)
In-Reply-To: <1901187.1613601279@warthog.procyon.org.uk>

On Wed, Feb 17, 2021 at 10:34:39PM +0000, David Howells wrote:
> Matthew Wilcox <willy@infradead.org> wrote:
> 
> > We're defeating the ondemand_readahead() algorithm here.  Let's suppose
> > userspace is doing 64kB reads, the filesystem is OrangeFS which only
> > wants to do 4MB reads, the page cache is initially empty and there's
> > only one thread doing a sequential read.  ondemand_readahead() calls
> > get_init_ra_size() which tells it to allocate 128kB and set the async
> > marker at 64kB.  Then orangefs calls readahead_expand() to allocate the
> > remainder of the 4MB.  After the app has read the first 64kB, it comes
> > back to read the next 64kB, sees the readahead marker and tries to trigger
> > the next batch of readahead, but it's already present, so it does nothing
> > (see page_cache_ra_unbounded() for what happens with pages present).
> 
> It sounds like Christoph is right on the right track and the vm needs to ask
> the filesystem (and by extension, the cache) before doing the allocation and
> before setting the trigger flag.  Then we don't need to call back into the vm
> to expand the readahead.

Doesn't work.  You could read my reply to Christoph, or try to figure out
how to get rid of
https://evilpiepirate.org/git/bcachefs.git/tree/fs/bcachefs/fs-io.c#n742
for yourself.

> Also, there's Steve's request to try and keep at least two requests in flight
> for CIFS/SMB at the same time to consider.

That's not relevant to this problem.

  reply	other threads:[~2021-02-17 22:53 UTC|newest]

Thread overview: 81+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-15 15:44 [PATCH 00/33] Network fs helper library & fscache kiocb API [ver #3] David Howells
2021-02-15 15:44 ` [PATCH 01/33] iov_iter: Add ITER_XARRAY David Howells
2021-02-15 15:44 ` [PATCH 02/33] mm: Add an unlock function for PG_private_2/PG_fscache David Howells
2021-02-16 10:26   ` Christoph Hellwig
2021-02-15 15:44 ` [PATCH 03/33] mm: Implement readahead_control pageset expansion David Howells
2021-02-16 10:32   ` Christoph Hellwig
2021-02-16 13:22     ` Matthew Wilcox
2021-02-17 14:36       ` Mike Marshall
2021-02-17 14:36         ` Mike Marshall
2021-02-17 15:42       ` David Howells
2021-02-17 16:59         ` Mike Marshall
2021-02-17 16:59           ` Mike Marshall
2021-02-17 22:20         ` David Howells
2021-02-16 11:48   ` David Howells
2021-02-17 16:13   ` Matthew Wilcox
2021-02-17 22:34   ` David Howells
2021-02-17 22:49     ` Matthew Wilcox [this message]
2021-02-18 17:47   ` David Howells
2021-02-15 15:45 ` [PATCH 04/33] vfs: Export rw_verify_area() for use by cachefiles David Howells
2021-02-16 10:26   ` Christoph Hellwig
2021-02-16 11:55   ` David Howells
2021-02-15 15:45 ` [PATCH 05/33] netfs: Make a netfs helper module David Howells
2021-02-15 15:45 ` [PATCH 06/33] netfs, mm: Move PG_fscache helper funcs to linux/netfs.h David Howells
2021-02-15 15:45 ` [PATCH 07/33] netfs, mm: Add unlock_page_fscache() and wait_on_page_fscache() David Howells
2021-02-15 15:45 ` [PATCH 08/33] netfs: Provide readahead and readpage netfs helpers David Howells
2021-02-15 15:45 ` [PATCH 09/33] netfs: Add tracepoints David Howells
2021-02-15 15:46 ` [PATCH 10/33] netfs: Gather stats David Howells
2021-02-15 15:46 ` [PATCH 11/33] netfs: Add write_begin helper David Howells
2021-02-15 15:46 ` [PATCH 12/33] netfs: Define an interface to talk to a cache David Howells
2021-02-15 15:46 ` [PATCH 13/33] netfs: Hold a ref on a page when PG_private_2 is set David Howells
2021-02-15 15:47 ` [PATCH 14/33] fscache, cachefiles: Add alternate API to use kiocb for read/write to cache David Howells
2021-02-16 10:49   ` Christoph Hellwig
2021-02-16 15:08   ` David Howells
2021-02-15 15:47 ` [PATCH 15/33] afs: Disable use of the fscache I/O routines David Howells
2021-02-15 15:47 ` [PATCH 16/33] afs: Pass page into dirty region helpers to provide THP size David Howells
2021-02-15 15:47 ` [PATCH 17/33] afs: Print the operation debug_id when logging an unexpected data version David Howells
2021-02-15 15:47 ` [PATCH 18/33] afs: Move key to afs_read struct David Howells
2021-02-15 15:47 ` [PATCH 19/33] afs: Don't truncate iter during data fetch David Howells
2021-02-15 15:48 ` [PATCH 20/33] afs: Log remote unmarshalling errors David Howells
2021-02-15 15:48 ` [PATCH 21/33] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2021-02-15 15:48 ` [PATCH 22/33] afs: Use ITER_XARRAY for writing David Howells
2021-02-15 15:48 ` [PATCH 23/33] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2021-02-15 15:49 ` [PATCH 24/33] afs: Extract writeback extension into its own function David Howells
2021-02-15 15:49 ` [PATCH 25/33] afs: Prepare for use of THPs David Howells
2021-02-15 15:49 ` [PATCH 26/33] afs: Use the fs operation ops to handle FetchData completion David Howells
2021-02-15 15:49 ` [PATCH 27/33] afs: Use new fscache read helper API David Howells
2021-02-15 15:49 ` [PATCH 28/33] ceph: disable old fscache readpage handling David Howells
2021-02-15 15:50 ` [PATCH 29/33] ceph: rework PageFsCache handling David Howells
2021-02-15 15:50 ` [PATCH 30/33] ceph: fix fscache invalidation David Howells
2021-02-15 15:50 ` [PATCH 31/33] ceph: convert readpage to fscache read helper David Howells
2021-02-15 15:50 ` [PATCH 32/33] ceph: plug write_begin into " David Howells
2021-02-15 15:51 ` [PATCH 33/33] ceph: convert ceph_readpages to ceph_readahead David Howells
2021-02-15 18:05 ` [PATCH 00/33] Network fs helper library & fscache kiocb API [ver #3] Jeff Layton
2021-02-15 18:05   ` Jeff Layton
2021-02-16  0:40   ` Steve French
2021-02-16  0:40     ` Steve French
2021-02-16  2:10     ` Matthew Wilcox
2021-02-16  5:18       ` Steve French
2021-02-16  5:18         ` Steve French
2021-02-16  5:22       ` Steve French
2021-02-16  5:22         ` Steve French
2021-02-23 20:27         ` Matthew Wilcox
2021-02-23 20:27           ` [f2fs-dev] " Matthew Wilcox
2021-02-24  4:57           ` Steve French
2021-02-24  4:57             ` [f2fs-dev] " Steve French
2021-02-24  4:57             ` Steve French
2021-02-24 13:32       ` David Howells
2021-02-24 15:51         ` Matthew Wilcox
2021-02-16 11:01     ` Jeff Layton
2021-02-16 11:01       ` Jeff Layton
2021-02-15 22:46 ` [PATCH 34/33] netfs: Use in_interrupt() not in_softirq() David Howells
2021-02-16  8:42   ` Christoph Hellwig
2021-02-16  9:06     ` Sebastian Andrzej Siewior
2021-02-16  9:29   ` David Howells
2021-02-16  9:30     ` Christoph Hellwig
2021-02-18 14:02     ` [PATCH 34/33] netfs: Pass flag rather than use in_softirq() David Howells
2021-02-18 15:06       ` Marc Dionne
2021-02-18 15:06         ` Marc Dionne
2021-02-18 15:16       ` Marc Dionne
2021-02-18 15:16         ` Marc Dionne
2021-02-19  9:01       ` Sebastian Andrzej Siewior

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