On 2017/7/1 上午4:43, bcache@xxxxxxxxxxxxxxxxxx wrote:
> From: Tang Junhui <tang.junhui@xxxxxxxxxx>
>
> In currently, we only alloc 6 open buckets for each cache set,
> but in usually, we always attach about 10 or so backend devices for
> each cache set, and the each bcache device are always accessed by
> about 10 or so threads in top application layer. So 6 open buckets
> are too few, It has led to that each of the same thread write data
> to different buckets, which would cause low efficiency write-back,
> and also cause buckets inefficient, and would be Very easy to run
> out of.
>
> I add debug message in bch_open_buckets_alloc() to print alloc bucket
> info, and test with ten bcache devices with a cache set, and each
> bcache device is accessed by ten threads.
>
> From the debug message, we can see that, after the modification, One
> bucket is more likely to assign to the same thread, and the data from
> the same thread are more likely to write the same bucket. Usually the
> same thread always write/read the same backend device, so it is good
> for write-back and also promote the usage efficiency of buckets.
>
> Signed-off-by: Tang Junhui <tang.junhui@xxxxxxxxxx>
Nice catch for performance !
Reviewed-by: Coly Li <colyli@xxxxxxx>
Thanks.
> ---
> drivers/md/bcache/alloc.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
> index ca4abe1..cacbe2d 100644
> --- a/drivers/md/bcache/alloc.c
> +++ b/drivers/md/bcache/alloc.c
> @@ -68,6 +68,8 @@
> #include <linux/random.h>
> #include <trace/events/bcache.h>
>
> +#define MAX_OPEN_BUCKETS 128
> +
> /* Bucket heap / gen */
>
> uint8_t bch_inc_gen(struct cache *ca, struct bucket *b)
> @@ -671,7 +673,7 @@ int bch_open_buckets_alloc(struct cache_set *c)
>
> spin_lock_init(&c->data_bucket_lock);
>
> - for (i = 0; i < 6; i++) {
> + for (i = 0; i < MAX_OPEN_BUCKETS; i++) {
> struct open_bucket *b = kzalloc(sizeof(*b), GFP_KERNEL);
> if (!b)
> return -ENOMEM;
>
--
Coly Li
