From: Guoqing Jiang <guoqing.jiang@linux.dev>
To: Logan Gunthorpe <logang@deltatee.com>,
linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
Song Liu <song@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
Stephen Bates <sbates@raithlin.com>,
Martin Oliveira <Martin.Oliveira@eideticom.com>,
David Sloan <David.Sloan@eideticom.com>
Subject: Re: [PATCH v2 09/12] md/raid5: Keep a reference to last stripe_head for batch
Date: Wed, 27 Apr 2022 09:36:59 +0800 [thread overview]
Message-ID: <56208e2a-5035-eb8e-c468-70b4dae66d5c@linux.dev> (raw)
In-Reply-To: <20220420195425.34911-10-logang@deltatee.com>
On 4/21/22 3:54 AM, Logan Gunthorpe wrote:
> When batching, every stripe head has to find the previous stripe head to
> add to the batch list. This involves taking the hash lock which is
> highly contended during IO.
>
> Instead of finding the previous stripe_head each time, store a
> reference to the previous stripe_head in a pointer so that it doesn't
> require taking the contended lock another time.
>
> The reference to the previous stripe must be released before scheduling
> and waiting for work to get done. Otherwise, it can hold up
> raid5_activate_delayed() and deadlock.
>
> Signed-off-by: Logan Gunthorpe<logang@deltatee.com>
> ---
> drivers/md/raid5.c | 51 +++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 39 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 0c250cc3bfff..28ea7b9b6ab6 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -843,7 +843,8 @@ static bool stripe_can_batch(struct stripe_head *sh)
> }
>
> /* we only do back search */
> -static void stripe_add_to_batch_list(struct r5conf *conf, struct stripe_head *sh)
> +static void stripe_add_to_batch_list(struct r5conf *conf,
> + struct stripe_head *sh, struct stripe_head *last_sh)
Nit, from stripe_add_to_batch_list's view, I think "head_sh" makes more
sense than
"last_sh".
> {
> struct stripe_head *head;
> sector_t head_sector, tmp_sec;
> @@ -856,15 +857,20 @@ static void stripe_add_to_batch_list(struct r5conf *conf, struct stripe_head *sh
> return;
> head_sector = sh->sector - RAID5_STRIPE_SECTORS(conf);
>
> - hash = stripe_hash_locks_hash(conf, head_sector);
> - spin_lock_irq(conf->hash_locks + hash);
> - head = find_get_stripe(conf, head_sector, conf->generation, hash);
> - spin_unlock_irq(conf->hash_locks + hash);
> -
> - if (!head)
> - return;
> - if (!stripe_can_batch(head))
> - goto out;
> + if (last_sh && head_sector == last_sh->sector) {
> + head = last_sh;
> + atomic_inc(&head->count);
> + } else {
> + hash = stripe_hash_locks_hash(conf, head_sector);
> + spin_lock_irq(conf->hash_locks + hash);
> + head = find_get_stripe(conf, head_sector, conf->generation,
> + hash);
> + spin_unlock_irq(conf->hash_locks + hash);
> + if (!head)
> + return;
> + if (!stripe_can_batch(head))
> + goto out;
> + }
>
> lock_two_stripes(head, sh);
> /* clear_batch_ready clear the flag */
> @@ -5800,6 +5806,7 @@ enum stripe_result {
>
> struct stripe_request_ctx {
> bool do_flush;
> + struct stripe_head *batch_last;
> };
>
> static enum stripe_result make_stripe_request(struct mddev *mddev,
> @@ -5889,8 +5896,13 @@ static enum stripe_result make_stripe_request(struct mddev *mddev,
> return STRIPE_SCHEDULE_AND_RETRY;
> }
>
> - if (stripe_can_batch(sh))
> - stripe_add_to_batch_list(conf, sh);
> + if (stripe_can_batch(sh)) {
> + stripe_add_to_batch_list(conf, sh, ctx->batch_last);
> + if (ctx->batch_last)
> + raid5_release_stripe(ctx->batch_last);
> + atomic_inc(&sh->count);
> + ctx->batch_last = sh;
> + }
>
> if (ctx->do_flush) {
> set_bit(STRIPE_R5C_PREFLUSH, &sh->state);
> @@ -5979,6 +5991,18 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
> } else if (res == STRIPE_RETRY) {
> continue;
> } else if (res == STRIPE_SCHEDULE_AND_RETRY) {
> + /*
> + * Must release the reference to batch_last before
> + * scheduling and waiting for work to be done,
> + * otherwise the batch_last stripe head could prevent
> + * raid5_activate_delayed() from making progress
> + * and thus deadlocking.
> + */
> + if (ctx.batch_last) {
> + raid5_release_stripe(ctx.batch_last);
> + ctx.batch_last = NULL;
> + }
> +
> schedule();
> prepare_to_wait(&conf->wait_for_overlap, &w,
> TASK_UNINTERRUPTIBLE);
> @@ -5990,6 +6014,9 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>
> finish_wait(&conf->wait_for_overlap, &w);
>
> + if (ctx.batch_last)
> + raid5_release_stripe(ctx.batch_last);
> +
> if (rw == WRITE)
> md_write_end(mddev);
> bio_endio(bi);
Otherwise looks good, Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Thanks,
Guoqing
next prev parent reply other threads:[~2022-04-27 1:37 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-20 19:54 [PATCH v2 00/12] Improve Raid5 Lock Contention Logan Gunthorpe
2022-04-20 19:54 ` [PATCH v2 01/12] md/raid5: Factor out ahead_of_reshape() function Logan Gunthorpe
2022-04-21 6:07 ` Christoph Hellwig
2022-04-21 9:17 ` Paul Menzel
2022-04-21 16:05 ` Logan Gunthorpe
2022-04-21 23:33 ` Wol
2022-04-27 1:28 ` Guoqing Jiang
2022-04-27 16:07 ` Logan Gunthorpe
2022-04-28 1:49 ` Guoqing Jiang
2022-04-28 15:44 ` Logan Gunthorpe
2022-04-29 0:24 ` Guoqing Jiang
2022-04-20 19:54 ` [PATCH v2 02/12] md/raid5: Refactor raid5_make_request loop Logan Gunthorpe
2022-04-21 6:08 ` Christoph Hellwig
2022-04-27 1:32 ` Guoqing Jiang
2022-04-27 16:08 ` Logan Gunthorpe
2022-04-28 1:16 ` Guoqing Jiang
2022-04-20 19:54 ` [PATCH v2 03/12] md/raid5: Move stripe_add_to_batch_list() call out of add_stripe_bio() Logan Gunthorpe
2022-04-27 1:33 ` Guoqing Jiang
2022-04-20 19:54 ` [PATCH v2 04/12] md/raid5: Move common stripe count increment code into __find_stripe() Logan Gunthorpe
2022-04-21 6:10 ` Christoph Hellwig
2022-04-27 1:33 ` Guoqing Jiang
2022-04-20 19:54 ` [PATCH v2 05/12] md/raid5: Factor out helper from raid5_make_request() loop Logan Gunthorpe
2022-04-21 6:14 ` Christoph Hellwig
2022-04-20 19:54 ` [PATCH v2 06/12] md/raid5: Drop the do_prepare flag in raid5_make_request() Logan Gunthorpe
2022-04-21 6:15 ` Christoph Hellwig
2022-04-27 2:11 ` Guoqing Jiang
2022-04-20 19:54 ` [PATCH v2 07/12] md/raid5: Move read_seqcount_begin() into make_stripe_request() Logan Gunthorpe
2022-04-21 6:15 ` Christoph Hellwig
2022-04-27 2:13 ` Guoqing Jiang
2022-04-20 19:54 ` [PATCH v2 08/12] md/raid5: Refactor for loop in raid5_make_request() into while loop Logan Gunthorpe
2022-04-21 6:16 ` Christoph Hellwig
2022-04-20 19:54 ` [PATCH v2 09/12] md/raid5: Keep a reference to last stripe_head for batch Logan Gunthorpe
2022-04-21 6:17 ` Christoph Hellwig
2022-04-27 1:36 ` Guoqing Jiang [this message]
2022-04-27 23:27 ` Logan Gunthorpe
2022-04-20 19:54 ` [PATCH v2 10/12] md/raid5: Refactor add_stripe_bio() Logan Gunthorpe
2022-04-21 6:18 ` Christoph Hellwig
2022-04-20 19:54 ` [PATCH v2 11/12] md/raid5: Check all disks in a stripe_head for reshape progress Logan Gunthorpe
2022-04-21 6:18 ` Christoph Hellwig
2022-04-27 1:53 ` Guoqing Jiang
2022-04-27 16:11 ` Logan Gunthorpe
2022-04-20 19:54 ` [PATCH v2 12/12] md/raid5: Pivot raid5_make_request() Logan Gunthorpe
2022-04-21 6:43 ` Christoph Hellwig
2022-04-21 15:54 ` Logan Gunthorpe
2022-04-27 2:06 ` Guoqing Jiang
2022-04-27 16:18 ` Logan Gunthorpe
2022-04-28 1:32 ` Guoqing Jiang
2022-04-21 8:45 ` [PATCH v2 00/12] Improve Raid5 Lock Contention Xiao Ni
2022-04-21 16:02 ` Logan Gunthorpe
2022-04-24 8:00 ` Guoqing Jiang
2022-04-25 15:39 ` Logan Gunthorpe
2022-04-25 16:12 ` Xiao Ni
2022-04-28 21:22 ` Logan Gunthorpe
2022-04-29 0:49 ` Guoqing Jiang
2022-04-29 16:01 ` Logan Gunthorpe
2022-04-30 1:44 ` Guoqing Jiang
2022-04-24 7:53 ` Guoqing Jiang
2022-04-25 15:37 ` Logan Gunthorpe
2022-04-25 23:07 ` Song Liu
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