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writeback: rework wb_[dec|inc]_stat family of functions

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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>
This commit is contained in:
Nikolay Borisov 2017-07-12 14:37:51 -07:00 committed by Linus Torvalds
parent c945dccc80
commit 3e8f399da4
4 changed files with 18 additions and 31 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
fs/fs-writeback.c
View file

@ -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);
}
}

24
include/linux/backing-dev.h
View file

@ -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)
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);
}
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)

7
lib/percpu_counter.c
View file

@ -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;

10
mm/page-writeback.c
View file

@ -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