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authorNikolay Borisov <nborisov@suse.com>2017-07-12 14:37:51 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-12 16:26:05 -0700
commit3e8f399da490e6ac20a3cfd6aa404c9aa961a9a2 (patch)
tree1e7ef3c2a6de595ad3d8d7f121b509f2ffeda371
parentc945dccc80856107f109c36a7d0e29a371b5d1b5 (diff)
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>
-rw-r--r--fs/fs-writeback.c8
-rw-r--r--include/linux/backing-dev.h24
-rw-r--r--lib/percpu_counter.c7
-rw-r--r--mm/page-writeback.c10
4 files changed, 18 insertions, 31 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8b426f83909f..245c430a2e41 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -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);
}
}
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 334165c911f0..854e1bdd0b2a 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -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)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 8ee7e5ec21be..3bf4a9984f4c 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -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;
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