On 2018/4/16 2:33 PM, tang.jun...@zte.com.cn wrote:
> From: Tang Junhui <tang.jun...@zte.com.cn>
> 
> In GC thread, we record the latest GC key in gc_done, which is expected
> to be used for incremental GC, but in currently code, we didn't realize
> it. When GC runs, front side IO would be blocked until the GC over, it
> would be a long time if there is a lot of btree nodes.
> 
> This patch realizes incremental GC, the main ideal is that, when there
> are front side I/Os, after GC some nodes (100), we stop GC, release locker
> of the btree node, and go to process the front side I/Os for some times
> (100 ms), then go back to GC again.
> 
> By this patch, when we doing GC, I/Os are not blocked all the time, and
> there is no obvious I/Os zero jump problem any more.
> 
> Patch v2: Rename some variables and macros name as Coly suggested.
> 
> Signed-off-by: Tang Junhui <tang.jun...@zte.com.cn>

Reviewed-by: Coly Li <col...@suse.de>

Thanks.

Coly Li

> ---
>  drivers/md/bcache/bcache.h  |  5 +++++
>  drivers/md/bcache/btree.c   | 15 ++++++++++++++-
>  drivers/md/bcache/request.c |  3 +++
>  3 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 843877e..5d52be8 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -445,6 +445,7 @@ struct cache {
>  
>  struct gc_stat {
>       size_t                  nodes;
> +     size_t                  nodes_pre;
>       size_t                  key_bytes;
>  
>       size_t                  nkeys;
> @@ -568,6 +569,10 @@ struct cache_set {
>        */
>       atomic_t                rescale;
>       /*
> +      * used for GC, identify if any front side I/Os is inflight
> +      */
> +     atomic_t                search_inflight;
> +     /*
>        * When we invalidate buckets, we use both the priority and the amount
>        * of good data to determine which buckets to reuse first - to weight
>        * those together consistently we keep track of the smallest nonzero
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 81e8dc3..6edb00e 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -90,6 +90,9 @@
>  
>  #define MAX_NEED_GC          64
>  #define MAX_SAVE_PRIO                72
> +#define MIN_GC_NODES         100
> +#define GC_SLEEP_MS          100
> +
>  
>  #define PTR_DIRTY_BIT                (((uint64_t) 1 << 36))
>  
> @@ -1581,6 +1584,13 @@ static int btree_gc_recurse(struct btree *b, struct 
> btree_op *op,
>               memmove(r + 1, r, sizeof(r[0]) * (GC_MERGE_NODES - 1));
>               r->b = NULL;
>  
> +             if (atomic_read(&b->c->search_inflight) &&
> +                 gc->nodes >= gc->nodes_pre + MIN_GC_NODES) {
> +                     gc->nodes_pre =  gc->nodes;
> +                     ret = -EAGAIN;
> +                     break;
> +             }
> +
>               if (need_resched()) {
>                       ret = -EAGAIN;
>                       break;
> @@ -1748,7 +1758,10 @@ static void bch_btree_gc(struct cache_set *c)
>               closure_sync(&writes);
>               cond_resched();
>  
> -             if (ret && ret != -EAGAIN)
> +             if (ret == -EAGAIN)
> +                     schedule_timeout_interruptible(msecs_to_jiffies
> +                                                    (GC_SLEEP_MS));
> +             else if (ret)
>                       pr_warn("gc failed!");
>       } while (ret);
>  
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 643c3021..a12afbc 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -637,7 +637,9 @@ static void do_bio_hook(struct search *s, struct bio 
> *orig_bio)
>  static void search_free(struct closure *cl)
>  {
>       struct search *s = container_of(cl, struct search, cl);
> +
>       bio_complete(s);
> +     atomic_dec(&s->d->c->search_inflight);
>  
>       if (s->iop.bio)
>               bio_put(s->iop.bio);
> @@ -655,6 +657,7 @@ static inline struct search *search_alloc(struct bio *bio,
>  
>       closure_init(&s->cl, NULL);
>       do_bio_hook(s, bio);
> +     atomic_inc(&d->c->search_inflight);
>  
>       s->orig_bio             = bio;
>       s->cache_miss           = NULL;
> 

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