writeback: rework wb_[dec|inc]_stat family of functions
authorNikolay Borisov <nborisov@suse.com>
Wed, 12 Jul 2017 21:37:51 +0000 (14:37 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 12 Jul 2017 23:26:05 +0000 (16:26 -0700)
commit3e8f399da490e6ac20a3cfd6aa404c9aa961a9a2
tree1e7ef3c2a6de595ad3d8d7f121b509f2ffeda371
parentc945dccc80856107f109c36a7d0e29a371b5d1b5
writeback: rework wb_[dec|inc]_stat family of functions

Currently the writeback statistics code uses a percpu counters to hold
various statistics.  Furthermore we have 2 families of functions - those
which disable local irq and those which doesn't and whose names begin
with double underscore.  However, they both end up calling
__add_wb_stats which in turn calls percpu_counter_add_batch which is
already irq-safe.

Exploiting this fact allows to eliminated the __wb_* functions since
they don't add any further protection than we already have.
Furthermore, refactor the wb_* function to call __add_wb_stat directly
without the irq-disabling dance.  This will likely result in better
runtime of code which deals with modifying the stat counters.

While at it also document why percpu_counter_add_batch is in fact
preempt and irq-safe since at least 3 people got confused.

Link: http://lkml.kernel.org/r/1498029937-27293-1-git-send-email-nborisov@suse.com
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/fs-writeback.c
include/linux/backing-dev.h
lib/percpu_counter.c
mm/page-writeback.c