linux-kernel - Re: [PATCH 2/2] Report the pagesize backing a VMA in /proc/pid/maps

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Date:	Sun, 5 Oct 2008 15:00:49 +0900
From:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
To:	"Alexey Dobriyan" <adobriyan@...il.com>
Cc:	"Mel Gorman" <mel@....ul.ie>, akpm@...ux-foundation.org,
	dave@...ux.vnet.ibm.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Report the pagesize backing a VMA in /proc/pid/maps

Hi

>> This patch adds a new field for hugepage-backed memory regions to show the
>> pagesize in /proc/pid/maps.  While the information is available in smaps,
>> maps is more human-readable and does not incur the cost of calculating Pss. An
>> example of a /proc/self/maps output for an application using hugepages with
>> this patch applied is;
>>
>> 08048000-0804c000 r-xp 00000000 03:01 49135      /bin/cat
>> 0804c000-0804d000 rw-p 00003000 03:01 49135      /bin/cat
>> 08400000-08800000 rw-p 00000000 00:10 4055       /mnt/libhugetlbfs.tmp.QzPPTJ (deleted) (hpagesize=4096kB)
>
>> To be predictable for parsers, the patch adds the notion of reporting on VMA
>> attributes by appending one or more fields that look like "(attribute)". This
>> already happens when a file is deleted and the user sees (deleted) after the
>> filename. The expectation is that existing parsers will not break as those
>> that read the filename should be reading forward after the inode number
>> and stopping when it sees something that is not part of the filename.
>> Parsers that assume everything after / is a filename will get confused by
>> (hpagesize=XkB) but are already broken due to (deleted).
>
> Looks like procps will start showing hpagesize tag as a mapping name
> (apologies for pasting crappy code):

Administrator expect mapping name is just file name when vma is
hugepage via mmap.
So, I feel Mel's code is nicer.

Thanks.
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