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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: 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>
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@ -380,8 +380,8 @@ static void inode_switch_wbs_work_fn(struct work_struct *work)
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struct page *page = radix_tree_deref_slot_protected(slot,
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&mapping->tree_lock);
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if (likely(page) && PageDirty(page)) {
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__dec_wb_stat(old_wb, WB_RECLAIMABLE);
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__inc_wb_stat(new_wb, WB_RECLAIMABLE);
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dec_wb_stat(old_wb, WB_RECLAIMABLE);
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inc_wb_stat(new_wb, WB_RECLAIMABLE);
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}
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}
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@ -391,8 +391,8 @@ static void inode_switch_wbs_work_fn(struct work_struct *work)
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&mapping->tree_lock);
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if (likely(page)) {
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WARN_ON_ONCE(!PageWriteback(page));
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__dec_wb_stat(old_wb, WB_WRITEBACK);
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__inc_wb_stat(new_wb, WB_WRITEBACK);
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dec_wb_stat(old_wb, WB_WRITEBACK);
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inc_wb_stat(new_wb, WB_WRITEBACK);
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}
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}
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@ -69,34 +69,14 @@ static inline void __add_wb_stat(struct bdi_writeback *wb,
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percpu_counter_add_batch(&wb->stat[item], amount, WB_STAT_BATCH);
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}
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static inline void __inc_wb_stat(struct bdi_writeback *wb,
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enum wb_stat_item item)
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static inline void inc_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
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{
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__add_wb_stat(wb, item, 1);
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}
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static inline void inc_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
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{
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unsigned long flags;
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local_irq_save(flags);
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__inc_wb_stat(wb, item);
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local_irq_restore(flags);
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}
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static inline void __dec_wb_stat(struct bdi_writeback *wb,
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enum wb_stat_item item)
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{
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__add_wb_stat(wb, item, -1);
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}
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static inline void dec_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
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{
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unsigned long flags;
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local_irq_save(flags);
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__dec_wb_stat(wb, item);
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local_irq_restore(flags);
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__add_wb_stat(wb, item, -1);
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}
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static inline s64 wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
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@ -72,6 +72,13 @@ void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
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}
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EXPORT_SYMBOL(percpu_counter_set);
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/**
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* This function is both preempt and irq safe. The former is due to explicit
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* preemption disable. The latter is guaranteed by the fact that the slow path
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* is explicitly protected by an irq-safe spinlock whereas the fast patch uses
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* this_cpu_add which is irq-safe by definition. Hence there is no need muck
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* with irq state before calling this one
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*/
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void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
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{
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s64 count;
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@ -601,7 +601,7 @@ static inline void __wb_writeout_inc(struct bdi_writeback *wb)
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{
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struct wb_domain *cgdom;
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__inc_wb_stat(wb, WB_WRITTEN);
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inc_wb_stat(wb, WB_WRITTEN);
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wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
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wb->bdi->max_prop_frac);
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@ -2435,8 +2435,8 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
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__inc_lruvec_page_state(page, NR_FILE_DIRTY);
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__inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
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__inc_node_page_state(page, NR_DIRTIED);
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__inc_wb_stat(wb, WB_RECLAIMABLE);
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__inc_wb_stat(wb, WB_DIRTIED);
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inc_wb_stat(wb, WB_RECLAIMABLE);
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inc_wb_stat(wb, WB_DIRTIED);
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task_io_account_write(PAGE_SIZE);
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current->nr_dirtied++;
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this_cpu_inc(bdp_ratelimits);
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@ -2741,7 +2741,7 @@ int test_clear_page_writeback(struct page *page)
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if (bdi_cap_account_writeback(bdi)) {
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struct bdi_writeback *wb = inode_to_wb(inode);
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__dec_wb_stat(wb, WB_WRITEBACK);
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dec_wb_stat(wb, WB_WRITEBACK);
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__wb_writeout_inc(wb);
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}
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}
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@ -2786,7 +2786,7 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
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page_index(page),
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PAGECACHE_TAG_WRITEBACK);
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if (bdi_cap_account_writeback(bdi))
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__inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
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inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
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/*
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* We can come through here when swapping anonymous
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