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-vzkWbYmk7l@https.bugzilla.kernel.org/>
Date:	Mon, 28 Sep 2015 15:23:46 +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 #4 from ValdikSS <iam@...dikss.org.ru> ---
Nobody really uses grep on sparse files. It was just a discussion on why many
people use cat|grep instead of just using 'grep file', as pipes are usually
slower. Somebody said that he uses cat|grep because it's actually faster than
'grep file' and made this test case. fallocate was used just to make big enough
file to tell a difference in seconds. His result was 1 second with cat|grep and
3 seconds with grep file, but he was running btrfs. When I tried his test case,
it hang grep so hard I couldn't kill it with SIGKILL even if it was in
'running' state. I took a look in strace what's going on and why it is stalled
and filled this bug.

Anyway, thanks for confirmation and acknowledgment this problem!

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