On Thu, 17 Nov 2016, David Rientjes wrote:
> On Thu, 17 Nov 2016, Douglas Anderson wrote:
>
> > diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
> > index b3ba142e59a4..885ba5482d9f 100644
> > --- a/drivers/md/dm-bufio.c
> > +++ b/drivers/md/dm-bufio.c
> > @@ -89,6 +89,7 @@ struct dm_bufio_client {
> >
> > struct list_head lru[LIST_SIZE];
> > unsigned long n_buffers[LIST_SIZE];
> > + unsigned long n_all_buffers;
> >
> > struct block_device *bdev;
> > unsigned block_size;
> > @@ -485,6 +486,7 @@ static void __link_buffer(struct dm_buffer *b, sector_t block, int dirty)
> > struct dm_bufio_client *c = b->c;
> >
> > c->n_buffers[dirty]++;
> > + c->n_all_buffers++;
> > b->block = block;
> > b->list_mode = dirty;
> > list_add(&b->lru_list, &c->lru[dirty]);
> > @@ -502,6 +504,7 @@ static void __unlink_buffer(struct dm_buffer *b)
> > BUG_ON(!c->n_buffers[b->list_mode]);
> >
> > c->n_buffers[b->list_mode]--;
> > + c->n_all_buffers--;
> > __remove(b->c, b);
> > list_del(&b->lru_list);
> > }
> > @@ -515,6 +518,7 @@ static void __relink_lru(struct dm_buffer *b, int dirty)
> >
> > BUG_ON(!c->n_buffers[b->list_mode]);
> >
> > + /* NOTE: don't update n_all_buffers: -1 + 1 = 0 */
> > c->n_buffers[b->list_mode]--;
> > c->n_buffers[dirty]++;
> > b->list_mode = dirty;
> > @@ -1588,17 +1592,10 @@ static unsigned long
> > dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
> > {
> > struct dm_bufio_client *c;
> > - unsigned long count;
> >
> > c = container_of(shrink, struct dm_bufio_client, shrinker);
> > - if (sc->gfp_mask & __GFP_FS)
> > - dm_bufio_lock(c);
> > - else if (!dm_bufio_trylock(c))
> > - return 0;
> >
> > - count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
> > - dm_bufio_unlock(c);
> > - return count;
> > + return c->n_all_buffers;
> > }
> >
> > /*
>
> Would be better to just avoid taking the mutex at all and returning
> c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY] with a comment that
> the estimate might be wrong, but the actual count may vary between
> ->count_objects() and ->scan_objects() anyway, so we don't actually care?
Yes - here I'm sending a patch that reads c->n_buffers without the lock.
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
dm-bufio: don't take the lock in dm_bufio_shrink_count
dm_bufio_shrink_count is called from do_shrink_slab to find out how many
freeable objects are there. The reported value doesn't have to be precise,
so we don't need to take the dm-bufio lock.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm-bufio.c | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
Index: linux-2.6/drivers/md/dm-bufio.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-bufio.c
+++ linux-2.6/drivers/md/dm-bufio.c
@@ -1587,18 +1587,9 @@ dm_bufio_shrink_scan(struct shrinker *sh
static unsigned long
dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
{
- struct dm_bufio_client *c;
- unsigned long count;
+ struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
- c = container_of(shrink, struct dm_bufio_client, shrinker);
- if (sc->gfp_mask & __GFP_FS)
- dm_bufio_lock(c);
- else if (!dm_bufio_trylock(c))
- return 0;
-
- count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
- dm_bufio_unlock(c);
- return count;
+ return ACCESS_ONCE(c->n_buffers[LIST_CLEAN]) + ACCESS_ONCE(c->n_buffers[LIST_DIRTY]);
}
/*
--
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