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Commit 3e8f399d authored by Nikolay Borisov's avatar Nikolay Borisov Committed by Linus Torvalds
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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: default avatarNikolay Borisov <nborisov@suse.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarJan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c945dccc

fs/fs-writeback.c

+4 −4
Original line number Diff line number Diff line
@@ -380,8 +380,8 @@ static void inode_switch_wbs_work_fn(struct work_struct *work) 
		struct page *page = radix_tree_deref_slot_protected(slot,

							&mapping->tree_lock);

		if (likely(page) && PageDirty(page)) {

			__dec_wb_stat(old_wb, WB_RECLAIMABLE);

			__inc_wb_stat(new_wb, WB_RECLAIMABLE);

			dec_wb_stat(old_wb, WB_RECLAIMABLE);

			inc_wb_stat(new_wb, WB_RECLAIMABLE);

		}

	}
@@ -391,8 +391,8 @@ static void inode_switch_wbs_work_fn(struct work_struct *work) 
							&mapping->tree_lock);

		if (likely(page)) {

			WARN_ON_ONCE(!PageWriteback(page));

			__dec_wb_stat(old_wb, WB_WRITEBACK);

			__inc_wb_stat(new_wb, WB_WRITEBACK);

			dec_wb_stat(old_wb, WB_WRITEBACK);

			inc_wb_stat(new_wb, WB_WRITEBACK);

		}

	}

include/linux/backing-dev.h

+2 −22
Original line number Diff line number Diff line
@@ -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)

{

	__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);

	__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)

lib/percpu_counter.c

+7 −0
Original line number Diff line number Diff line
@@ -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;

mm/page-writeback.c

+5 −5
Original line number Diff line number Diff line
@@ -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