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From: Mel Gorman <mgorman@suse.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, Minchan Kim <minchan@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints
Date: Tue, 3 Feb 2015 10:50:07 +0000	[thread overview]
Message-ID: <20150203105007.GP2395@suse.de> (raw)
In-Reply-To: <20150202143541.1efdd2b571413200cb9a4698@linux-foundation.org>

On Mon, Feb 02, 2015 at 02:35:41PM -0800, Andrew Morton wrote:
> On Mon, 2 Feb 2015 22:18:24 +0000 Mel Gorman <mgorman@suse.de> wrote:
> 
> > > Is there something
> > > preventing this from being addressed within glibc?
> >  
> > I doubt it other than I expect they'll punt it back and blame either the
> > application for being stupid or the kernel for being slow.
> 
> *Is* the application being stupid?  What is it actually doing? 

Only a little. There is little simulated think time between the allocation
and the subsequent free. It means the cost of alloc/free dominates where
in "real" applications they would either be reusing buffers if they were
constantly needed or the think time would mask the cost of the free.

> Something like
> 
> pthread_routine()
> {
> 	p = malloc(X);
> 	do_some(work);
> 	free(p);
> 	return;
> }
> 

Pretty much. There is a search_mem() function that

alloc(copy_size)
memcpy
search
free(copy)

A real application might try and avoid the copy or reuse buffers if they
encountered this particular problem.

-- 
Mel Gorman
SUSE Labs

  parent reply	other threads:[~2015-02-03 10:50 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 [this message]
2015-02-05 21:44     ` Rik van Riel
2015-02-02 22:22 ` Dave Hansen
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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