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>

1 files changed, 5 insertions, 5 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0b60cc7ddac2..96e93b214d31 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -601,7 +601,7 @@ static inline void __wb_writeout_inc(struct bdi_writeback *wb)
 {
         struct wb_domain *cgdom;
 
-        __inc_wb_stat(wb, WB_WRITTEN);
+        inc_wb_stat(wb, WB_WRITTEN);
         wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
                                wb->bdi->max_prop_frac);
 
@@ -2435,8 +2435,8 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
                 __inc_lruvec_page_state(page, NR_FILE_DIRTY);
                 __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
                 __inc_node_page_state(page, NR_DIRTIED);
-                __inc_wb_stat(wb, WB_RECLAIMABLE);
-                __inc_wb_stat(wb, WB_DIRTIED);
+                inc_wb_stat(wb, WB_RECLAIMABLE);
+                inc_wb_stat(wb, WB_DIRTIED);
                 task_io_account_write(PAGE_SIZE);
                 current->nr_dirtied++;
                 this_cpu_inc(bdp_ratelimits);
@@ -2741,7 +2741,7 @@ int test_clear_page_writeback(struct page *page)
                         if (bdi_cap_account_writeback(bdi)) {
                                 struct bdi_writeback *wb = inode_to_wb(inode);
 
-                                __dec_wb_stat(wb, WB_WRITEBACK);
+                                dec_wb_stat(wb, WB_WRITEBACK);
                                 __wb_writeout_inc(wb);
                         }
                 }
@@ -2786,7 +2786,7 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
                                                 page_index(page),
                                                 PAGECACHE_TAG_WRITEBACK);
                         if (bdi_cap_account_writeback(bdi))
-                                __inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
+                                inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
 
                         /*
                          * We can come through here when swapping anonymous