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From: Dave Hansen <dave.hansen@intel.com>
To: Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org
Cc: Minchan Kim <minchan@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints
Date: Mon, 02 Feb 2015 14:22:36 -0800	[thread overview]
Message-ID: <54CFF8AC.6010102@intel.com> (raw)
In-Reply-To: <20150202165525.GM2395@suse.de>

On 02/02/2015 08:55 AM, Mel Gorman wrote:
> This patch identifies when a thread is frequently calling MADV_DONTNEED
> on the same region of memory and starts ignoring the hint. On an 8-core
> single-socket machine this was the impact on ebizzy using glibc 2.19.

The manpage, at least, claims that we zero-fill after MADV_DONTNEED is
called:

>      MADV_DONTNEED
>               Do  not  expect  access in the near future.  (For the time being, the application is finished with the given range, so the kernel can free resources
>               associated with it.)  Subsequent accesses of pages in this range will succeed, but will result either in reloading of the memory contents  from  the
>               underlying mapped file (see mmap(2)) or zero-fill-on-demand pages for mappings without an underlying file.

So if we have anything depending on the behavior that it's _always_
zero-filled after an MADV_DONTNEED, this will break it.

  parent reply	other threads:[~2015-02-02 22:22 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-02 16:55 Mel Gorman
2015-02-02 22:05 ` Andrew Morton
2015-02-02 22:18   ` Mel Gorman
2015-02-02 22:35     ` Andrew Morton
2015-02-03  0:26       ` Davidlohr Bueso
2015-02-03 10:50       ` Mel Gorman
2015-02-05 21:44     ` Rik van Riel
2015-02-02 22:22 ` Dave Hansen [this message]
2015-02-03  8:19   ` MADV_DONTNEED semantics? Was: " Vlastimil Babka
2015-02-03 10:53     ` Kirill A. Shutemov
2015-02-03 11:42       ` Vlastimil Babka
2015-02-03 16:20         ` Michael Kerrisk (man-pages)
2015-02-04 13:46           ` Vlastimil Babka
2015-02-04 14:00             ` Michael Kerrisk (man-pages)
2015-02-04 17:02               ` Vlastimil Babka
2015-02-04 19:24                 ` Michael Kerrisk (man-pages)
2015-02-05  1:07                   ` Minchan Kim
2015-02-06 15:41                     ` Michael Kerrisk (man-pages)
2015-02-09  6:46                       ` Minchan Kim
2015-02-09  9:13                         ` Michael Kerrisk (man-pages)
2015-02-05 15:41                   ` Michal Hocko
2015-02-06 15:57                     ` Michael Kerrisk (man-pages)
2015-02-06 20:45                       ` Michal Hocko
2015-02-09  6:50                       ` Minchan Kim
2015-02-04  0:09         ` Minchan Kim
2015-02-03 11:16     ` Mel Gorman
2015-02-03 15:21       ` Michal Hocko
2015-02-03 16:25         ` Michael Kerrisk (man-pages)
2015-02-03  9:47   ` Mel Gorman
2015-02-03 10:47     ` Kirill A. Shutemov
2015-02-03 11:21       ` Mel Gorman

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