On Sun, Jul 03, 2016 at 10:24:55PM -0400, Theodore Ts'o wrote:

From bf21c027d84ded545d2c08fa01fd184d29641458 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Sun, 3 Jul 2016 22:20:49 -0400
Subject: [PATCH] ext4: in ext4_setattr(), only call ext4_truncate() if there is no data to drop

If there are no blocks associated with the inode (and no inline data),
there's no point calling ext4_truncate().  This avoids setting the
replace-via-truncate hueristic if there is an attempt to truncate a
file which is already zero-length --- which is something that happens
in the core dumping code, in case there is an already existing core
file.  In the comon case, there is not a previous core file, so by not
enabling the replace-via-truncate hueristic, we can speed up core
dumps.

Reported-by: Omar Sandoval <redacted>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

This patch is buggy; when I tried running regression tests, it failed
early.  So you probably want to skip this.

					- Ted