linux-kernel - Re: [PATCH] mm: page_alloc: Avoid marking zones full prematurely after zone

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Message-ID: <20130409101437.GE29860@dhcp22.suse.cz>
Date:	Tue, 9 Apr 2013 12:14:37 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hedi Berriche <hedi@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: Avoid marking zones full prematurely
 after zone_reclaim()

On Tue 09-04-13 18:05:30, Simon Jeons wrote:
[...]
> >I try this in v3.9-rc5:
> >dd if=/dev/sda of=/dev/null bs=1MB
> >14813+0 records in
> >14812+0 records out
> >14812000000 bytes (15 GB) copied, 105.988 s, 140 MB/s
> >
> >free -m -s 1
> >
> >                   total       used       free     shared buffers
> >cached
> >Mem:          7912       1181       6731          0 663        239
> >-/+ buffers/cache:        277       7634
> >Swap:         8011          0       8011
> >
> >It seems that almost 15GB copied before I stop dd, but the used
> >pages which I monitor during dd always around 1200MB. Weird, why?
> >
> 
> Sorry for waste your time, but the test result is weird, is it?

I am not sure which values you have been watching but you have to
realize that you are reading a _partition_ not a file and those pages
go into buffers rather than the page chache.
-- 
Michal Hocko
SUSE Labs
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