From: Mark Goodwin <goodwinos@gmail.com>
To: Mark Seger <mjseger@gmail.com>
Cc: Nathan Scott <nathans@redhat.com>, xfs@oss.sgi.com
Subject: Re: definitions for /proc/fs/xfs/stat
Date: Tue, 18 Jun 2013 10:13:30 +1000 [thread overview]
Message-ID: <51BFA62A.5040900@gmail.com> (raw)
In-Reply-To: <419435719.1662203.1371431489790.JavaMail.root@redhat.com>
On 06/17/2013 11:11 AM, Nathan Scott wrote:
>> ok, I have a simple reproducer. try out the following, noting you'll
>> obviously have to change the directory pointed to by dname:
>>
>> libc=ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
>> falloc=getattr(libc, 'fallocate')
>>
>
> This is using the glibc fallocate wrapper - I have vague memories of an
> old libc which used to do per-page buffered writes providing a poor-mans
> implementation of fallocate, maybe somehow that older version/behaviour
> is being triggered.
Python probably tipped you into a posix_fallocate() bog hole - it writes
one byte to every block in the range offset .. offset+len as the portable
(but poor-man's) implementation of fallocate(). This combined with your
controller cache could explain the unexpected i/o.
See glibc:sysdeps/posix/posix_fallocate.c
-- Mark
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next prev parent reply other threads:[~2013-06-18 0:13 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-14 16:37 definitions for /proc/fs/xfs/stat Mark Seger
2013-06-14 22:16 ` Nathan Scott
2013-06-14 22:37 ` Mark Seger
2013-06-15 0:17 ` Nathan Scott
2013-06-15 1:55 ` Mark Seger
2013-06-15 2:04 ` Dave Chinner
2013-06-15 10:35 ` Mark Seger
2013-06-15 16:22 ` Mark Seger
2013-06-16 0:11 ` Dave Chinner
2013-06-16 12:58 ` Mark Seger
2013-06-16 22:06 ` Dave Chinner
2013-06-16 22:31 ` Mark Seger
2013-06-16 23:14 ` Dave Chinner
2013-06-16 23:31 ` Mark Seger
2013-06-17 1:11 ` Nathan Scott
2013-06-17 2:46 ` Dave Chinner
2013-06-17 5:41 ` Nathan Scott
2013-06-17 10:57 ` Mark Seger
2013-06-17 11:13 ` Dave Chinner
2013-06-17 14:57 ` Mark Seger
2013-06-17 20:28 ` Stefan Ring
2013-06-18 0:15 ` Dave Chinner
2013-06-18 10:17 ` Mark Seger
2013-06-19 23:02 ` Useful stats (was Re: definitions for /proc/fs/xfs/stat) Nathan Scott
2013-06-17 11:19 ` definitions for /proc/fs/xfs/stat Dave Chinner
2013-06-17 13:18 ` Stan Hoeppner
2013-06-18 0:13 ` Mark Goodwin [this message]
2013-06-16 0:00 ` Dave Chinner
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