linux-ext4 - [Bug 105121] lseek(SEEK_DATA) hangs for a long time for sparse files in the page cache

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Message-ID: <bug-105121-13602-AQKdWQF0gI@https.bugzilla.kernel.org/>
Date:	Mon, 28 Sep 2015 15:15:29 +0000
From:	bugzilla-daemon@...zilla.kernel.org
To:	linux-ext4@...r.kernel.org
Subject: [Bug 105121] lseek(SEEK_DATA) hangs for a long time for sparse files
 in the page cache

https://bugzilla.kernel.org/show_bug.cgi?id=105121

--- Comment #3 from Theodore Tso <tytso@....edu> ---
This implies that grep is using lseek(SEEK_DATA) as an optimization when users
use grep on sparse files.   So I'm guessing this is a Thing, but I'm at a loss
why people are interested in running grep on a sparse file (with or without
blocks preallocated using fallocate).   Can you enlighten me as to why people
(or at least you and your colleague) find it useful to run grep on such files?

Not that it matters since this is a pretty clear optimization we should add to
ext4; I'm just curious what the use case is.

Thanks!!

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