Re: [PATCH] mm: page_alloc: Avoid marking zones full prematurelyafter zone_reclaim()

From: Michal Hocko
Date: Thu Mar 21 2013 - 04:19:13 EST

On Thu 21-03-13 10:33:07, Simon Jeons wrote:
> Hi Mel,
> On 03/21/2013 02:19 AM, Mel Gorman wrote:
> >The following problem was reported against a distribution kernel when
> >zone_reclaim was enabled but the same problem applies to the mainline
> >kernel. The reproduction case was as follows
> >
> >1. Run numactl -m +0 dd if=largefile of=/dev/null
> > This allocates a large number of clean pages in node 0
> I confuse why this need allocate a large number of clean pages?

It reads from file and puts pages into the page cache. The pages are not
modified so they are clean. Output file is /dev/null so no pages are
written. dd doesn't call fadvise(POSIX_FADV_DONTNEED) on the input file
by default so pages from the file stay in the page cache
Michal Hocko
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