From: Tobias Diedrich <ranma+kernel@tdiedrich.de>
To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Subject: posix_fadvise/WILLNEED synchronous on fuse/sshfs instead of async?
Date: Wed, 11 Nov 2009 16:19:37 +0100 [thread overview]
Message-ID: <20091111151937.GC20655@yumi.tdiedrich.de> (raw)
While trying to use posix_fadvise(...POSIX_FADVISE_WILLNEED) to
implement userspace read-ahead (with a bigger read-ahead window than
the kernel default) I found that if the underlying filesystem is
fuse/sshfs posix_fadvise is no longer doing asynchronous reads:
strace -tt with mnt/testfile on sshfs and server with very slow
upstream (ADSL):
5345 00:00:17.334209 open("mnt/testfile", O_RDONLY|O_LARGEFILE) = 3
5345 00:00:18.011383 _llseek(3, 0, [3544379], SEEK_END) = 0
5345 00:00:18.011626 _llseek(3, 0, [0], SEEK_SET) = 0
5345 00:00:18.012393 fadvise64_64(3, 0, 1048576, POSIX_FADV_WILLNEED) = 0
5345 00:01:02.438097 write(1, "[file] File size is 3544379 byte"..., 34) = 34
Note that fadvise takes 40 seconds...
Is this expected behaviour?
I would have expected that fadvise is always asynchronous and I
could rely on the call to return almost immediately.
--
Tobias PGP: http://8ef7ddba.uguu.de
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next reply other threads:[~2009-11-11 15:19 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-11 15:19 Tobias Diedrich [this message]
2009-11-11 15:43 ` Miklos Szeredi
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