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writeback: rework wb_[dec|inc]_stat family of functions

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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>
This commit is contained in:
Nikolay Borisov 2017-07-12 14:37:51 -07:00 • committed by Linus Torvalds
parent c945dccc80
commit 3e8f399da4
4 changed files with 18 additions and 31 deletions
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24
include/linux/backing-dev.h
View file

@ -69,34 +69,14 @@ static inline void __add_wb_stat(struct bdi_writeback *wb,
percpu_counter_add_batch(&wb->stat[item], amount, WB_STAT_BATCH);
}
static inline void __inc_wb_stat(struct bdi_writeback *wb,
enum wb_stat_item item)
static inline void inc_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
{
__add_wb_stat(wb, item, 1);
}
static inline void inc_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
{
unsigned long flags;
local_irq_save(flags);
__inc_wb_stat(wb, item);
local_irq_restore(flags);
}
static inline void __dec_wb_stat(struct bdi_writeback *wb,
enum wb_stat_item item)
{
__add_wb_stat(wb, item, -1);
}
static inline void dec_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
{
unsigned long flags;
local_irq_save(flags);
__dec_wb_stat(wb, item);
local_irq_restore(flags);
__add_wb_stat(wb, item, -1);
}
static inline s64 wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)