Hi Tang Junhui---
I'm not really sure about this one. It changes the semantics of the
amount of work done-- nr_to_scan now means number of things to free
instead of the number to check.
If the system is under severe memory pressure, and most of the cache is
essential/actively used, this could greatly increase the amount of work
done.
As to the i < btree_cache_used, it's arguably a bug, but it only reduces
the amount of work done if the cache is very, very small.
Mike
On 01/30/2018 06:46 PM, tang.junhui@xxxxxxxxxx wrote:
> From: Tang Junhui <tang.junhui@xxxxxxxxxx>
>
> In bch_mca_scan(), nr btree nodes are expected to shrink, so the for(;;)
> loop need to satisfy the condition freed < nr.
> And since c->btree_cache_used always decrease after mca_data_free() calling
> in for(;;) loop, so we need a auto variable to record c->btree_cache_used
> before the for(;;) loop.
>
> Signed-off-by: Tang Junhui <tang.junhui@xxxxxxxxxx>
> ---
> drivers/md/bcache/btree.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 81e8dc3..7e9ef3d 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -664,6 +664,7 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
> struct btree *b, *t;
> unsigned long i, nr = sc->nr_to_scan;
> unsigned long freed = 0;
> + unsigned int btree_cache_used;
>
> if (c->shrinker_disabled)
> return SHRINK_STOP;
> @@ -700,7 +701,8 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
> }
> }
>
> - for (i = 0; (nr--) && i < c->btree_cache_used; i++) {
> + btree_cache_used = c->btree_cache_used;
> + for (i = 0; freed < nr && i < btree_cache_used; i++) {
> if (list_empty(&c->btree_cache))
> goto out;
>
>
