linux-kernel - Re: Regarding memory fragmentation using malloc....

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Message-ID: <BANLkTi=7KHMA_JOwQcMQj5M+XU=qO07s2g@mail.gmail.com>
Date:	Wed, 13 Apr 2011 19:44:39 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Pintu Agarwal <pintu_agarwal@...oo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Changli Gao <xiaosuo@...il.com>, Jiri Slaby <jslaby@...e.cz>,
	azurIt <azurit@...ox.sk>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Jiri Slaby <jirislaby@...il.com>
Subject: Re: Regarding memory fragmentation using malloc....

On Wed, Apr 13, 2011 at 2:54 PM, Pintu Agarwal <pintu_agarwal@...oo.com> wrote:
> Dear All,
>
> I am trying to understand how memory fragmentation occurs in linux using many malloc calls.
> I am trying to reproduce the page fragmentation problem in linux 2.6.29.x on a linux mobile(without Swap) using a small malloc(in loop) test program of BLOCK_SIZE (64*(4*K)).
> And then monitoring the page changes in /proc/buddyinfo after each operation.
> From the output I can see that the page values under buddyinfo keeps changing. But I am not able to relate these changes with my malloc BLOCK_SIZE.
> I mean with my BLOCK_SIZE of (2^6 x 4K ==> 2^6 PAGES) the 2^6 th block under /proc/buddyinfo should change. But this is not the actual behaviour.
> Whatever is the blocksize, the buddyinfo changes only for 2^0 or 2^1 or 2^2 or 2^3.
>
> I am trying to measure the level of fragmentation after each page allocation.
> Can somebody explain me in detail, how actually /proc/buddyinfo changes after each allocation and deallocation.
>

What malloc() sees is virtual memory of the process, while buddyinfo
shows physical memory pages.

When you malloc() 64K memory, the kernel may not allocate a 64K
physical memory at one time
for you.

Thanks.
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