From mboxrd@z Thu Jan 1 00:00:00 1970 From: Coly Li Subject: [RFC PATCH 16/16] bcache: avoid extra memory consumption in struct bbio for large bucket size Date: Sun, 5 Jul 2020 23:56:01 +0800 Message-ID: <20200705155601.5404-17-colyli@suse.de> References: <20200705155601.5404-1-colyli@suse.de> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: Received: from mx2.suse.de ([195.135.220.15]:38342 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727790AbgGEP4s (ORCPT ); Sun, 5 Jul 2020 11:56:48 -0400 In-Reply-To: <20200705155601.5404-1-colyli@suse.de> Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: linux-bcache@vger.kernel.org Cc: linux-block@vger.kernel.org, Coly Li Bcache uses struct bbio to do I/Os for meta data pages like uuids, disk_buckets, prio_buckets, and btree nodes. Example writing a btree node onto cache device, the process is, - Allocate a struct bbio from mempool c->bio_meta. - Inside struct bbio embedded a struct bio, initialize bi_inline_vecs for this embedded bio. - Call bch_bio_map() to map each meta data page to each bv from the inlined bi_io_vec table. - Call bch_submit_bbio() to submit the bio into underlying block layer. - When the I/O completed, only release the struct bbio, don't touch the reference counter of the meta data pages. The struct bbio is defined as, 738 struct bbio { 739 unsigned int submit_time_us; [snipped] 748 struct bio bio; 749 }; Because struct bio is embedded at the end of struct bbio, therefore the actual size of struct bbio is sizeof(struct bio) + size of the embedded bio->bi_inline_vecs. Now all the meta data bucket size are limited to meta_bucket_pages(), if the bucket size is large than meta_bucket_pages()*PAGE_SECTORS, rested space in the bucket is unused. Therefore the most used space in meta bucket is (1<bio_meta as, mempool_init_kmalloc_pool(&c->bio_meta, 2, sizeof(struct bbio) + sizeof(struct bio_vec) * bucket_pages(c)) It is too large, neither the Linux buddy allocator cannot allocate so much continuous pages, nor the extra allocated pages are wasted. This patch replace bucket_pages() to meta_bucket_pages() in two places, - In bch_cache_set_alloc(), when initialize mempool c->bio_meta, uses sizeof(struct bbio) + sizeof(struct bio_vec) * bucket_pages(c) to set the allocating object size. - In bch_bbio_alloc(), when calling bio_init() to set inline bvec talbe bi_inline_bvecs, uses meta_bucket_pages() to indicate number of the inline bio vencs number. Now the maximum size of embedded bio inside struct bbio exactly matches the limit of meta_bucket_pages(), no extra page wasted. Signed-off-by: Coly Li --- drivers/md/bcache/io.c | 2 +- drivers/md/bcache/super.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c index b25ee33b0d0b..a14a445618b4 100644 --- a/drivers/md/bcache/io.c +++ b/drivers/md/bcache/io.c @@ -26,7 +26,7 @@ struct bio *bch_bbio_alloc(struct cache_set *c) struct bbio *b = mempool_alloc(&c->bio_meta, GFP_NOIO); struct bio *bio = &b->bio; - bio_init(bio, bio->bi_inline_vecs, bucket_pages(c)); + bio_init(bio, bio->bi_inline_vecs, meta_bucket_pages(&c->sb)); return bio; } diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 6766d426e933..eac4998dddc1 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -1913,7 +1913,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb) if (mempool_init_kmalloc_pool(&c->bio_meta, 2, sizeof(struct bbio) + - sizeof(struct bio_vec) * bucket_pages(c))) + sizeof(struct bio_vec) * meta_bucket_pages(&c->sb))) goto err; if (mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size)) -- 2.26.2