Commit 7490a2d2 authored by Shakeel Butt's avatar Shakeel Butt Committed by Linus Torvalds
Browse files

writeback: memcg: simplify cgroup_writeback_by_id 

Currently cgroup_writeback_by_id calls mem_cgroup_wb_stats() to get dirty
pages for a memcg.  However mem_cgroup_wb_stats() does a lot more than
just get the number of dirty pages.  Just directly get the number of dirty
pages instead of calling mem_cgroup_wb_stats().  Also
cgroup_writeback_by_id() is only called for best-effort dirty flushing, so
remove the unused 'nr' parameter and no need to explicitly flush memcg
stats.

Link: https://lkml.kernel.org/r/20210722182627.2267368-1-shakeelb@google.com


Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7ae12c80

fs/fs-writeback.c

+9 −11
Original line number Diff line number Diff line
@@ -1039,20 +1039,20 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi, 
 * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs

 * @bdi_id: target bdi id

 * @memcg_id: target memcg css id

 * @nr: number of pages to write, 0 for best-effort dirty flushing

 * @reason: reason why some writeback work initiated

 * @done: target wb_completion

 *

 * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id

 * with the specified parameters.

 */

int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,

int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,

			   enum wb_reason reason, struct wb_completion *done)

{

	struct backing_dev_info *bdi;

	struct cgroup_subsys_state *memcg_css;

	struct bdi_writeback *wb;

	struct wb_writeback_work *work;

	unsigned long dirty;

	int ret;



	/* lookup bdi and memcg */
@@ -1081,24 +1081,22 @@ int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr, 
	}



	/*

	 * If @nr is zero, the caller is attempting to write out most of

	 * The caller is attempting to write out most of

	 * the currently dirty pages.  Let's take the current dirty page

	 * count and inflate it by 25% which should be large enough to

	 * flush out most dirty pages while avoiding getting livelocked by

	 * concurrent dirtiers.

	 *

	 * BTW the memcg stats are flushed periodically and this is best-effort

	 * estimation, so some potential error is ok.

	 */

	if (!nr) {

		unsigned long filepages, headroom, dirty, writeback;



		mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,

				      &writeback);

		nr = dirty * 10 / 8;

	}

	dirty = memcg_page_state(mem_cgroup_from_css(memcg_css), NR_FILE_DIRTY);

	dirty = dirty * 10 / 8;



	/* issue the writeback work */

	work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);

	if (work) {

		work->nr_pages = nr;

		work->nr_pages = dirty;

		work->sync_mode = WB_SYNC_NONE;

		work->range_cyclic = 1;

		work->reason = reason;

include/linux/memcontrol.h

+15 −0
Original line number Diff line number Diff line
@@ -955,6 +955,16 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg, 
	local_irq_restore(flags);

}



static inline unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)

{

	long x = READ_ONCE(memcg->vmstats.state[idx]);

#ifdef CONFIG_SMP

	if (x < 0)

		x = 0;

#endif

	return x;

}



static inline unsigned long lruvec_page_state(struct lruvec *lruvec,

					      enum node_stat_item idx)

{
@@ -1391,6 +1401,11 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg, 
{

}



static inline unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)

{

	return 0;

}



static inline unsigned long lruvec_page_state(struct lruvec *lruvec,

					      enum node_stat_item idx)

{

include/linux/writeback.h

+1 −1
Original line number Diff line number Diff line
@@ -218,7 +218,7 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc, 
void wbc_detach_inode(struct writeback_control *wbc);

void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,

			      size_t bytes);

int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages,

int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,

			   enum wb_reason reason, struct wb_completion *done);

void cgroup_writeback_umount(void);

bool cleanup_offline_cgwb(struct bdi_writeback *wb);

mm/memcontrol.c

+1 −12
Original line number Diff line number Diff line
@@ -645,17 +645,6 @@ void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val) 
	cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id());

}



/* idx can be of type enum memcg_stat_item or node_stat_item. */

static unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)

{

	long x = READ_ONCE(memcg->vmstats.state[idx]);

#ifdef CONFIG_SMP

	if (x < 0)

		x = 0;

#endif

	return x;

}



/* idx can be of type enum memcg_stat_item or node_stat_item. */

static unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx)

{
@@ -4668,7 +4657,7 @@ void mem_cgroup_flush_foreign(struct bdi_writeback *wb) 
		    atomic_read(&frn->done.cnt) == 1) {

			frn->at = 0;

			trace_flush_foreign(wb, frn->bdi_id, frn->memcg_id);

			cgroup_writeback_by_id(frn->bdi_id, frn->memcg_id, 0,

			cgroup_writeback_by_id(frn->bdi_id, frn->memcg_id,

					       WB_REASON_FOREIGN_FLUSH,

					       &frn->done);

		}