diff options
| author | Nikolay Borisov | 2017-07-12 14:37:51 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2017-07-12 16:26:05 -0700 |
| commit | 3e8f399da490e6ac20a3cfd6aa404c9aa961a9a2 (patch) | |
| tree | 1e7ef3c2a6de595ad3d8d7f121b509f2ffeda371 /lib | |
| parent | c945dccc80856107f109c36a7d0e29a371b5d1b5 (diff) | |
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>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/percpu_counter.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index 8ee7e5ec21be..3bf4a9984f4c 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -72,6 +72,13 @@ void percpu_counter_set(struct percpu_counter *fbc, s64 amount) } EXPORT_SYMBOL(percpu_counter_set); +/** + * This function is both preempt and irq safe. The former is due to explicit + * preemption disable. The latter is guaranteed by the fact that the slow path + * is explicitly protected by an irq-safe spinlock whereas the fast patch uses + * this_cpu_add which is irq-safe by definition. Hence there is no need muck + * with irq state before calling this one + */ void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch) { s64 count; |