This is a backport of the following upstream commit.
commit 0b732828091a545185ad13d0b2e6800600788d61
Author: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>
Date: Tue Jun 10 13:57:29 2014 +0900
[PATCH 3/3] Stop maximizing the bitmap buffer to reduce the risk of OOM.
We tried to maximize the bitmap buffer to get the best performance,
but the performance degradation caused by multi-cycle processing
looks very small according to the benchmark on 2TB memory:
https://lkml.org/lkml/2013/3/26/914
This result means we don't need to make an effort to maximize the
bitmap buffer, it will just increase the risk of OOM.
This patch sets a small fixed value (4MB) as a safety limit,
it may be safer and enough in most cases.
Signed-off-by: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>
Signed-off-by: Baoquan He <bhe@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
