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From: David Howells <>
To: Matthew Wilcox <>
	Rohith Surabattula <>,
	Steve French <>,
	Shyam Prasad N <>,, Jeff Layton <>,,,
Subject: Re: [PATCH 14/14] mm, netfs, fscache: Stop read optimisation when folio removed from pagecache
Date: Thu, 07 Apr 2022 07:41:47 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Matthew Wilcox <> wrote:

> On Thu, Apr 07, 2022 at 12:05:05AM +0100, David Howells wrote:
> > Fix this by adding an extra address_space operation, ->removing folio(),
> > and flag, AS_NOTIFY_REMOVING_FOLIO.  The operation is called if the flag is
> > set when a folio is removed from the pagecache.  The flag should be set if
> > a non-NULL cookie is obtained from fscache and cleared in ->evict_inode()
> > before truncate_inode_pages_final() is called.
> What's wrong with ->freepage?

It's too late.  The optimisation must be cancelled before there's a chance
that a new page can be allocated and attached to the pagecache - but
->freepage() is called after the folio has been removed.  Doing it in
->freepage() would allow ->readahead(), ->readpage() or ->write_begin() to
jump in and start a new read (which gets skipped because the optimisation is
still in play).

Another possibility could be that the FSCACHE_COOKIE_HAVE_DATA and
FSCACHE_COOKIE_NO_DATA_TO_READ flags could be moved from cookie->flags to
mapping->flags and the VM could do the twiddling itself (no aop required) -
except that fscache can't currently then find them (maybe use an aop for


  parent reply	other threads:[~2022-04-07  6:42 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-06 23:02 [PATCH 00/14] cifs: Iterators, netfslib and folios David Howells
2022-04-06 23:02 ` [PATCH 01/14] cifs: Add some helper functions David Howells
2022-04-06 23:02 ` [PATCH 02/14] cifs: Add a function to read into an iter from a socket David Howells
2022-04-06 23:03 ` [PATCH 03/14] cifs: Check the IOCB_DIRECT flag, not O_DIRECT David Howells
2022-04-06 23:03 ` [PATCH 04/14] cifs: Change the I/O paths to use an iterator rather than a page list David Howells
2022-04-06 23:03 ` [PATCH 05/14] cifs: Remove unused code David Howells
2022-04-06 23:03 ` [PATCH 06/14] cifs: Use netfslib to handle reads David Howells
2022-04-06 23:04 ` [PATCH 07/14] cifs: Share server EOF pos with netfslib David Howells
2022-04-06 23:04 ` [PATCH 08/14] netfs: Allow the netfs to make the io (sub)request alloc larger David Howells
2022-04-06 23:04 ` [PATCH 09/14] cifs: Put credits into cifs_io_subrequest, not on the stack David Howells
2022-04-06 23:04 ` [PATCH 10/14] cifs: Hold the open file on netfs_io_request, not netfs_io_subrequest David Howells
2022-04-06 23:04 ` [PATCH 11/14] cifs: Clamp length according to credits and rsize David Howells
2022-04-06 23:04 ` [PATCH 12/14] cifs: Expose netfs subrequest debug ID and index in read tracepoints David Howells
2022-04-06 23:04 ` [PATCH 13/14] cifs: Split the smb3_add_credits tracepoint David Howells
2022-04-06 23:05 ` [PATCH 14/14] mm, netfs, fscache: Stop read optimisation when folio removed from pagecache David Howells
2022-04-07  3:13   ` Matthew Wilcox
2022-04-07  6:41   ` David Howells [this message]
2022-04-07 21:22     ` Matthew Wilcox
2022-04-25 12:07     ` David Howells
2022-04-25 12:30       ` Matthew Wilcox
2022-09-02  0:30         ` David Wysochanski

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