On 2019/7/27 6:19 下午, Yaowei Bai wrote: > The interface cache_available_percent is used to indicate how > many buckets in percent are available to be used to cache data > at a specific moment. It should include the unused and clean > buckets which we get from bch_btree_gc_finish function: > > if (!GC_MARK(b) || GC_MARK(b) == GC_MARK_RECLAIMABLE) > c->avail_nbuckets++; > > However currently in the allocation code we didn't distinguish > these available buckets with the metadata and dirty buckets, we > just decrease the c->avail_nbuckets everytime we allocate a bucket, > and correct it after a gc completes. With this, in a read-only > scenario, you can observe that cache_available_percent bounces, > it first go down to a number, like 95, and then bounces back to > 100. It goes on and on, making users confused.
Hmm, I don't feel it could be confused, indeed I feel this is what is designed for, counting both data/meta data buckets allocation. We can document in admin-guide/bcache.rst, and notice people that even for read-only requests, buckets can also be allocated for metadata. Thanks. Coly Li > > This patch fixes this problem by decreasing c->avail_nbuckets > only when allocate metadata and dirty buckets. With this patch, > cache_available_percent will always be accurate and avoid the > confusion. > > Signed-off-by: Yaowei Bai <[email protected]> > --- > drivers/md/bcache/alloc.c | 10 +++++----- > drivers/md/bcache/request.c | 9 ++++++++- > 2 files changed, 13 insertions(+), 6 deletions(-) > > diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c > index 609df38..dc7f6c2 100644 > --- a/drivers/md/bcache/alloc.c > +++ b/drivers/md/bcache/alloc.c > @@ -443,17 +443,17 @@ long bch_bucket_alloc(struct cache *ca, unsigned int > reserve, bool wait) > SET_GC_MARK(b, GC_MARK_METADATA); > SET_GC_MOVE(b, 0); > b->prio = BTREE_PRIO; > + > + if (ca->set->avail_nbuckets > 0) { > + ca->set->avail_nbuckets--; > + bch_update_bucket_in_use(ca->set, &ca->set->gc_stats); > + } > } else { > SET_GC_MARK(b, GC_MARK_RECLAIMABLE); > SET_GC_MOVE(b, 0); > b->prio = INITIAL_PRIO; > } > > - if (ca->set->avail_nbuckets > 0) { > - ca->set->avail_nbuckets--; > - bch_update_bucket_in_use(ca->set, &ca->set->gc_stats); > - } > - > return r; > } > > diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c > index 41adcd1..b69bd8d 100644 > --- a/drivers/md/bcache/request.c > +++ b/drivers/md/bcache/request.c > @@ -244,9 +244,16 @@ static void bch_data_insert_start(struct closure *cl) > if (op->writeback) { > SET_KEY_DIRTY(k, true); > > - for (i = 0; i < KEY_PTRS(k); i++) > + for (i = 0; i < KEY_PTRS(k); i++) { > SET_GC_MARK(PTR_BUCKET(op->c, k, i), > GC_MARK_DIRTY); > + > + if (op->c->avail_nbuckets > 0) { > + op->c->avail_nbuckets--; > + bch_update_bucket_in_use(op->c, > + > &op->c->gc_stats); > + } > + } > } > > SET_KEY_CSUM(k, op->csum); >
