From: Shakeel Butt <shakeelb@xxxxxxxxxx> Subject: 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@xxxxxxxxxx Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/fs-writeback.c | 20 +++++++++----------- include/linux/memcontrol.h | 15 +++++++++++++++ include/linux/writeback.h | 2 +- mm/memcontrol.c | 13 +------------ 4 files changed, 26 insertions(+), 24 deletions(-) --- a/fs/fs-writeback.c~writeback-memcg-simplify-cgroup_writeback_by_id +++ a/fs/fs-writeback.c @@ -1039,20 +1039,20 @@ restart: * 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, i } /* - * 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; --- a/include/linux/memcontrol.h~writeback-memcg-simplify-cgroup_writeback_by_id +++ a/include/linux/memcontrol.h @@ -955,6 +955,16 @@ static inline void mod_memcg_state(struc 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(struc { } +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) { --- a/include/linux/writeback.h~writeback-memcg-simplify-cgroup_writeback_by_id +++ a/include/linux/writeback.h @@ -218,7 +218,7 @@ void wbc_attach_and_unlock_inode(struct 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); --- a/mm/memcontrol.c~writeback-memcg-simplify-cgroup_writeback_by_id +++ a/mm/memcontrol.c @@ -646,17 +646,6 @@ void __mod_memcg_state(struct mem_cgroup } /* 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) { long x = 0; @@ -4668,7 +4657,7 @@ void mem_cgroup_flush_foreign(struct bdi 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); } _
