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[5.186.122.168]) by smtp.gmail.com with ESMTPSA id z40sm4847371edz.86.2019.02.04.22.51.02 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 04 Feb 2019 22:51:02 -0800 (PST) From: =?UTF-8?q?Javier=20Gonz=C3=A1lez?= To: mb@lightnvm.io Cc: hans.holmberg@cnexlabs.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, =?UTF-8?q?Javier=20Gonz=C3=A1lez?= Subject: [PATCH V3] lightnvm: pblk: prevent stall due to wb threshold Date: Tue, 5 Feb 2019 07:50:42 +0100 Message-Id: <20190205065042.6727-1-javier@javigon.com> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org In order to respect mw_cuinits, pblk's write buffer maintains a backpointer to protect data not yet persisted; when writing to the write buffer, this backpointer defines a threshold that pblk's rate-limiter enforces. On small PU configurations, the following scenarios might take place: (i) the threshold is larger than the write buffer and (ii) the threshold is smaller than the write buffer, but larger than the maximun allowed split bio - 256KB at this moment (Note that writes are not always split - we only do this when we the size of the buffer is smaller than the buffer). In both cases, pblk's rate-limiter prevents the I/O to be written to the buffer, thus stalling. This patch fixes the original backpointer implementation by considering the threshold both on buffer creation and on the rate-limiters path, when bio_split is triggered (case (ii) above). Fixes: 766c8ceb16fc ("lightnvm: pblk: guarantee that backpointer is respected on writer stall") Signed-off-by: Javier González --- Changes since V1: - Fix a bad arithmetinc on the rate-limiter max_io calculation (from Hans) Changes since V2: - Address case where mw_cunits = 0 in the new math drivers/lightnvm/pblk-rb.c | 25 +++++++++++++++++++------ drivers/lightnvm/pblk-rl.c | 5 ++--- drivers/lightnvm/pblk.h | 2 +- 3 files changed, 22 insertions(+), 10 deletions(-) diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c index d4ca8c64ee0f..a6133b50ed9c 100644 --- a/drivers/lightnvm/pblk-rb.c +++ b/drivers/lightnvm/pblk-rb.c @@ -45,10 +45,23 @@ void pblk_rb_free(struct pblk_rb *rb) /* * pblk_rb_calculate_size -- calculate the size of the write buffer */ -static unsigned int pblk_rb_calculate_size(unsigned int nr_entries) +static unsigned int pblk_rb_calculate_size(unsigned int nr_entries, + unsigned int threshold) { - /* Alloc a write buffer that can at least fit 128 entries */ - return (1 << max(get_count_order(nr_entries), 7)); + unsigned int thr_sz = 1 << (get_count_order(threshold + NVM_MAX_VLBA)); + unsigned int max_sz = max(thr_sz, nr_entries); + unsigned int max_io; + + /* Alloc a write buffer that can (i) fit at least two split bios + * (considering max I/O size NVM_MAX_VLBA, and (ii) guarantee that the + * threshold will be respected + */ + max_io = (1 << max((int)(get_count_order(max_sz)), + (int)(get_count_order(NVM_MAX_VLBA << 1)))); + if ((threshold + NVM_MAX_VLBA) >= max_io) + max_io <<= 1; + + return max_io; } /* @@ -67,12 +80,12 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold, unsigned int alloc_order, order, iter; unsigned int nr_entries; - nr_entries = pblk_rb_calculate_size(size); + nr_entries = pblk_rb_calculate_size(size, threshold); entries = vzalloc(array_size(nr_entries, sizeof(struct pblk_rb_entry))); if (!entries) return -ENOMEM; - power_size = get_count_order(size); + power_size = get_count_order(nr_entries); power_seg_sz = get_count_order(seg_size); down_write(&pblk_rb_lock); @@ -149,7 +162,7 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold, * Initialize rate-limiter, which controls access to the write buffer * by user and GC I/O */ - pblk_rl_init(&pblk->rl, rb->nr_entries); + pblk_rl_init(&pblk->rl, rb->nr_entries, threshold); return 0; } diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c index 76116d5f78e4..b014957dde0b 100644 --- a/drivers/lightnvm/pblk-rl.c +++ b/drivers/lightnvm/pblk-rl.c @@ -207,7 +207,7 @@ void pblk_rl_free(struct pblk_rl *rl) del_timer(&rl->u_timer); } -void pblk_rl_init(struct pblk_rl *rl, int budget) +void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold) { struct pblk *pblk = container_of(rl, struct pblk, rl); struct nvm_tgt_dev *dev = pblk->dev; @@ -217,7 +217,6 @@ void pblk_rl_init(struct pblk_rl *rl, int budget) int sec_meta, blk_meta; unsigned int rb_windows; - /* Consider sectors used for metadata */ sec_meta = (lm->smeta_sec + lm->emeta_sec[0]) * l_mg->nr_free_lines; blk_meta = DIV_ROUND_UP(sec_meta, geo->clba); @@ -234,7 +233,7 @@ void pblk_rl_init(struct pblk_rl *rl, int budget) /* To start with, all buffer is available to user I/O writers */ rl->rb_budget = budget; rl->rb_user_max = budget; - rl->rb_max_io = budget >> 1; + rl->rb_max_io = threshold ? (budget - threshold) : (budget - 1); rl->rb_gc_max = 0; rl->rb_state = PBLK_RL_HIGH; diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h index 72ae8755764e..a6386d5acd73 100644 --- a/drivers/lightnvm/pblk.h +++ b/drivers/lightnvm/pblk.h @@ -924,7 +924,7 @@ int pblk_gc_sysfs_force(struct pblk *pblk, int force); /* * pblk rate limiter */ -void pblk_rl_init(struct pblk_rl *rl, int budget); +void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold); void pblk_rl_free(struct pblk_rl *rl); void pblk_rl_update_rates(struct pblk_rl *rl); int pblk_rl_high_thrs(struct pblk_rl *rl); -- 2.17.1