performance/read-ahead: stricter adherence to force-atime-update

Throwaway read-ahead cache in fstat only if force-atime-update is
set. Note that fstat flushes read-ahead cache only for atime
consistency. However if atime consistency is needed user is required
to set force-atime-update which updates atime on backend fs even
though application reads are served from read-ahead cache. So, if user
has not set force-atime-update, atime won't be accurate and there is
no point in flushing read-ahead cache in fstats. mounts
requiring atime consistency have to mandatorily set
force-atime-update.

Also note that normally kernel interspers reads with fstat. So,
read-ahead is not effective as fstats flush read-ahead-cache. Instead
it regresses performance due to wasted network reads. It is
recommended to turn off read-ahead if applications require atime
consistency.

This patch is aimed at applications which don't require atime
consistency. Without atime consistency required, read-ahead cache is
effective and increases performance of sequential reads.

Change-Id: I122bbc410cee96661823f9c4b934383495c18446
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Fixes: bz#1601166

0 files changed, 0 insertions, 0 deletions