From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Ben Gamari <bgamari.foss@gmail.com>
Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org,
rsync@lists.samba.org, linux-mm@kvack.org
Subject: Re: fadvise DONTNEED implementation (or lack thereof)
Date: Tue, 9 Nov 2010 16:28:02 +0900 (JST) [thread overview]
Message-ID: <20101109162525.BC87.A69D9226@jp.fujitsu.com> (raw)
In-Reply-To: <87lj597hp9.fsf@gmail.com>
> I've recently been trying to track down the root cause of my server's
> persistent issue of thrashing horribly after being left inactive. It
> seems that the issue is likely my nightly backup schedule (using rsync)
> which traverses my entire 50GB home directory. I was surprised to find
> that rsync does not use fadvise to notify the kernel of its use-once
> data usage pattern.
>
> It looks like a patch[1] was written (although never merged, it seems)
> incorporating fadvise support, but I found its implementation rather
> odd, using mincore() and FADV_DONTNEED to kick out only regions brought
> in by rsync. It seemed to me the simpler and more appropriate solution
> would be to simply flag every touched file with FADV_NOREUSE and let the
> kernel manage automatically expelling used pages.
>
> After looking deeper into the kernel implementation[2] of fadvise() the
> reason for using DONTNEED became more apparant. It seems that the kernel
> implements NOREUSE as a noop. A little googling revealed[3] that I not
> the first person to encounter this limitation. It looks like a few
> folks[4] have discussed addressing the issue in the past, but nothing
> has happened as of 2.6.36. Are there plans to implement this
> functionality in the near future? It seems like the utility of fadvise
> is severely limited by lacking support for NOREUSE.
btw, Other OSs seems to also don't implement it.
example,
http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/lib/libc/port/gen/posix_fadvise.c
35 /*
36 * SUSv3 - file advisory information
37 *
38 * This function does nothing, but that's OK because the
39 * Posix specification doesn't require it to do anything
40 * other than return appropriate error numbers.
41 *
42 * In the future, a file system dependent fadvise() or fcntl()
43 * interface, similar to madvise(), should be developed to enable
44 * the kernel to optimize I/O operations based on the given advice.
45 */
46
47 /* ARGSUSED1 */
48 int
49 posix_fadvise(int fd, off_t offset, off_t len, int advice)
50 {
51 struct stat64 statb;
52
53 switch (advice) {
54 case POSIX_FADV_NORMAL:
55 case POSIX_FADV_RANDOM:
56 case POSIX_FADV_SEQUENTIAL:
57 case POSIX_FADV_WILLNEED:
58 case POSIX_FADV_DONTNEED:
59 case POSIX_FADV_NOREUSE:
60 break;
61 default:
62 return (EINVAL);
63 }
64 if (len < 0)
65 return (EINVAL);
66 if (fstat64(fd, &statb) != 0)
67 return (EBADF);
68 if (S_ISFIFO(statb.st_mode))
69 return (ESPIPE);
70 return (0);
71 }
So, I don't think application developers will use fadvise() aggressively
because we don't have a cross platform agreement of a fadvice behavior.
next prev parent reply other threads:[~2010-11-09 7:28 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-04 5:58 fadvise DONTNEED implementation (or lack thereof) Ben Gamari
2010-11-09 7:28 ` KOSAKI Motohiro [this message]
2010-11-09 8:03 ` KOSAKI Motohiro
2010-11-09 12:54 ` Ben Gamari
2010-11-14 5:09 ` KOSAKI Motohiro
2010-11-14 5:20 ` Ben Gamari
2010-11-14 21:33 ` Brian K. White
2010-11-15 6:07 ` Minchan Kim
2010-11-15 7:09 ` KOSAKI Motohiro
2010-11-15 7:19 ` Minchan Kim
2010-11-15 7:28 ` KOSAKI Motohiro
2010-11-15 7:46 ` Minchan Kim
2010-11-15 12:46 ` Ben Gamari
2010-11-15 8:47 ` Peter Zijlstra
2010-11-15 9:05 ` Minchan Kim
2010-11-15 14:48 ` Rik van Riel
2010-11-17 10:16 ` Minchan Kim
2010-11-17 11:15 ` Minchan Kim
2010-11-17 16:22 ` Rik van Riel
2010-11-18 2:47 ` Minchan Kim
2010-11-18 3:24 ` Rik van Riel
2010-11-18 3:46 ` Minchan Kim
2010-11-15 9:10 ` KOSAKI Motohiro
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