linux-kernel - Re: [PATCH] tmpfs: support SEEK_DATA and SEEK

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Date:	Thu, 29 Nov 2012 21:17:51 +0100
From:	Jim Meyering <jim@...ering.net>
To:	Dave Chinner <david@...morbit.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Jaegeuk Hanse <jaegeuk.hanse@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Ts'o <tytso@....edu>,
	Zheng Liu <wenqing.lz@...bao.com>,
	Jeff liu <jeff.liu@...cle.com>,
	Paul Eggert <eggert@...ucla.edu>,
	Christoph Hellwig <hch@...radead.org>,
	Josef Bacik <josef@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andreas Dilger <adilger@...ger.ca>,
	Marco Stornelli <marco.stornelli@...il.com>,
	Chris Mason <chris.mason@...ionio.com>,
	Sunil Mushran <sunil.mushran@...cle.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] tmpfs: support SEEK_DATA and SEEK_HOLE (reprise)

Dave Chinner wrote:
...
>> So, yes, GNU cp will soon use this feature.
>
> It would be nice if utilities like grep used it, too, because having
> grep burn gigabytes of memory scanning holes in large files and
> then going OOM is, well, kind of nasty:
>
> $ xfs_io -f -c "truncate 1t" blah
> $ ls -l
> total 0
> -rw-r--r-- 1 dave dave 1.0T Nov 30 06:42 blah
> $ grep foo blah
> grep: memory exhausted
> $ $ grep -V
> grep (GNU grep) 2.12

Hi Dave,

Yes, adapting grep is also on the road map.
That precise case was one of my arguments for making SEEK_DATA/SEEK_HOLE
support more widespread.
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