On 17/03/2018 4:58 PM, tang.junhui@xxxxxxxxxx wrote: > From: Tang Junhui <tang.junhui@xxxxxxxxxx> > > We make a lot of effort to sort buckets in heap, but we only pull > half of buckets into free_inc queue, it's too wasteful. > > And in incremental GC, we may run out of all buckets in free_inc > queue during GC, so it would be useful if we have more buckets > in free_inc queue. > > This patch enlarge the size of free_inc queue as much as the heap. > > Signed-off-by: Tang Junhui <tang.junhui@xxxxxxxxxx> > --- > drivers/md/bcache/super.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c > index b4d2892..6f428c0 100644 > --- a/drivers/md/bcache/super.c > +++ b/drivers/md/bcache/super.c > @@ -1835,7 +1835,7 @@ static int cache_alloc(struct cache *ca) > !init_fifo_exact(&ca->free[RESERVE_PRIO], prio_buckets(ca), GFP_KERNEL) || > !init_fifo(&ca->free[RESERVE_MOVINGGC], free, GFP_KERNEL) || > !init_fifo(&ca->free[RESERVE_NONE], free, GFP_KERNEL) || > - !init_fifo(&ca->free_inc, free << 2, GFP_KERNEL) || > + !init_fifo(&ca->free_inc, free << 3, GFP_KERNEL) || > !init_heap(&ca->heap, free << 3, GFP_KERNEL) || > !(ca->buckets = vzalloc(sizeof(struct bucket) * > ca->sb.nbuckets)) || > Hi Junhui, I feel the original code might be better. ca->heap is not a strict ordered list, it just makes sure at some location in the heap list, all prios before this location are larger than all prios after this location. If ca->heap is x2 size of ca->free_inc, it means there is chance to invalidate 50% buckets of higher prios. And the buckets with lower prios can still stay in ca->heap until they have chance to be selected. If ca->free_inc is set to same size as ca->heap, we need to know that not all buckets in ca->heap can be invalidated, so after iterating all buckets in ca->heap, maybe we can not make ca->free_inc to be full. In this case, gc thread needs to be waken up. This will be a bug because it is very probably that not all buckets from ca->heap can be pushed into ca->free_inc, then gc thread is just frequently waken up for nothing. Thanks. Coly Li
