Messages in this thread Patch in this message | | | Subject | Re: [PATCH 0/9] blk-mq: Reduce static requests memory footprint for shared sbitmap | From | John Garry <> | Date | Tue, 20 Jul 2021 18:05:42 +0100 |
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On 20/07/2021 16:22, Ming Lei wrote: > On Wed, Jul 14, 2021 at 11:06:26PM +0800, John Garry wrote: >> Currently a full set of static requests are allocated per hw queue per >> tagset when shared sbitmap is used. >> >> However, only tagset->queue_depth number of requests may be active at >> any given time. As such, only tagset->queue_depth number of static >> requests are required. >> >> The same goes for using an IO scheduler, which allocates a full set of >> static requests per hw queue per request queue. >> >> This series very significantly reduces memory usage in both scenarios by >> allocating static rqs per tagset and per request queue, respectively, >> rather than per hw queue per tagset and per request queue. >> >> For megaraid sas driver on my 128-CPU arm64 system with 1x SATA disk, we >> save approx. 300MB(!) [370MB -> 60MB] >> >> A couple of patches are marked as RFC, as maybe there is a better >> implementation approach.
Hi Ming,
To be clear, my concerns with my implementation were: a. Interface of __blk_mq_{alloc,free}_rqs was a bit strange in passing a struct list_head * and struct request ** . But maybe it's ok. b. We need to ensure that the host should not expect a set of static rqs per hw queue, i.e. should not use blk_mq_ops.init_request hctx_idx argument. The guard I have added is effectively useless against that. I am thinking that we should have a variant of blk_mq_ops.init_request without a hctx_idx argument, which needs to be used for shared sbitmap.
> > There is another candidate for addressing this issue, and looks simpler:
Thanks, I think that this solution does not deal with b., above, either.
> > block/blk-mq-sched.c | 4 ++++ > block/blk-mq-tag.c | 4 ++++ > block/blk-mq-tag.h | 3 +++ > block/blk-mq.c | 18 ++++++++++++++++++ > block/blk-mq.h | 11 +++++++++++ > 5 files changed, 40 insertions(+) > > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c > index c838d81ac058..b9236ee0fe4e 100644 > --- a/block/blk-mq-sched.c > +++ b/block/blk-mq-sched.c > @@ -538,6 +538,10 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q, > if (!hctx->sched_tags) > return -ENOMEM; > > + blk_mq_set_master_tags(hctx->sched_tags, > + q->queue_hw_ctx[0]->sched_tags, hctx->flags, > + hctx_idx); > + > ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests); > if (ret) > blk_mq_sched_free_tags(set, hctx, hctx_idx); > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 86f87346232a..c471a073234d 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -608,6 +608,10 @@ int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx, > tags->nr_reserved_tags, set->flags); > if (!new) > return -ENOMEM; > + > + blk_mq_set_master_tags(new, > + hctx->queue->queue_hw_ctx[0]->sched_tags, set->flags, > + hctx->queue_num); > ret = blk_mq_alloc_rqs(set, new, hctx->queue_num, tdepth); > if (ret) { > blk_mq_free_rq_map(new, set->flags); > diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h > index 8ed55af08427..0a3fbbc61e06 100644 > --- a/block/blk-mq-tag.h > +++ b/block/blk-mq-tag.h > @@ -21,6 +21,9 @@ struct blk_mq_tags { > struct request **static_rqs; > struct list_head page_list; > > + /* only used for blk_mq_is_sbitmap_shared() */ > + struct blk_mq_tags *master;
It is a bit odd to have a pointer to struct blk_mq_tags in struct blk_mq_tags like this
> + > /* > * used to clear request reference in rqs[] before freeing one > * request pool > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 2c4ac51e54eb..ef8a6a7e5f7c 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2348,6 +2348,15 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, > { > struct page *page; > > + if (blk_mq_is_sbitmap_shared(set->flags)) { > + if (tags->master) > + tags = tags->master; > + if (hctx_idx < set->nr_hw_queues - 1) { > + blk_mq_clear_rq_mapping(set, tags, hctx_idx); > + return; > + } > + } > + > if (tags->rqs && set->ops->exit_request) { > int i; > > @@ -2444,6 +2453,12 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, > size_t rq_size, left; > int node; > > + if (blk_mq_is_sbitmap_shared(set->flags) && tags->master) { > + memcpy(tags->static_rqs, tags->master->static_rqs, > + sizeof(tags->static_rqs[0]) * tags->nr_tags); > + return 0; > + } > + > node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx); > if (node == NUMA_NO_NODE) > node = set->numa_node; > @@ -2860,6 +2875,9 @@ static bool __blk_mq_alloc_map_and_request(struct blk_mq_tag_set *set, > if (!set->tags[hctx_idx]) > return false; > > + blk_mq_set_master_tags(set->tags[hctx_idx], set->tags[0], flags, > + hctx_idx); > + > ret = blk_mq_alloc_rqs(set, set->tags[hctx_idx], hctx_idx, > set->queue_depth); > if (!ret) > diff --git a/block/blk-mq.h b/block/blk-mq.h > index d08779f77a26..a08b89be6acc 100644 > --- a/block/blk-mq.h > +++ b/block/blk-mq.h > @@ -354,5 +354,16 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx, > return __blk_mq_active_requests(hctx) < depth; > } > > +static inline void blk_mq_set_master_tags(struct blk_mq_tags *tags, > + struct blk_mq_tags *master_tags, unsigned int flags, > + unsigned int hctx_idx) > +{ > + if (blk_mq_is_sbitmap_shared(flags)) { > + if (hctx_idx) > + tags->master = master_tags; > + else > + tags->master = NULL; > + } > +} > > #endif >
I'll check this solution a bit further.
Thanks, John
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