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Message-ID: <fefeda56-6b28-45b8-bc35-75f537613142@molgen.mpg.de>
Date: Sun, 27 Apr 2025 11:51:31 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: hch@...radead.org, axboe@...nel.dk, xni@...hat.com, agk@...hat.com,
snitzer@...nel.org, mpatocka@...hat.com, song@...nel.org,
yukuai3@...wei.com, cl@...ux.com, nadav.amit@...il.com, ubizjak@...il.com,
akpm@...ux-foundation.org, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, dm-devel@...ts.linux.dev,
linux-raid@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com,
johnny.chenyi@...wei.com
Subject: Re: [PATCH v2 8/9] md: fix is_mddev_idle()
Dear Kuai,
Thank you for your patch.
Am 27.04.25 um 10:29 schrieb Yu Kuai:
> From: Yu Kuai <yukuai3@...wei.com>
>
> If sync_speed is above speed_min, then is_mddev_idle() will be called
> for each sync IO to check if the array is idle, and inflihgt sync_io
infli*gh*t
> will be limited if the array is not idle.
>
> However, while mkfs.ext4 for a large raid5 array while recovery is in
> progress, it's found that sync_speed is already above speed_min while
> lots of stripes are used for sync IO, causing long delay for mkfs.ext4.
>
> Root cause is the following checking from is_mddev_idle():
>
> t1: submit sync IO: events1 = completed IO - issued sync IO
> t2: submit next sync IO: events2 = completed IO - issued sync IO
> if (events2 - events1 > 64)
>
> For consequence, the more sync IO issued, the less likely checking will
> pass. And when completed normal IO is more than issued sync IO, the
> condition will finally pass and is_mddev_idle() will return false,
> however, last_events will be updated hence is_mddev_idle() can only
> return false once in a while.
>
> Fix this problem by changing the checking as following:
>
> 1) mddev doesn't have normal IO completed;
> 2) mddev doesn't have normal IO inflight;
> 3) if any member disks is partition, and all other partitions doesn't
> have IO completed.
Do you have benchmarks of mkfs.ext4 before and after your patch? It’d be
great if you added those.
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> drivers/md/md.c | 84 +++++++++++++++++++++++++++----------------------
> drivers/md/md.h | 3 +-
> 2 files changed, 48 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 541151bcfe81..955efe0b40c6 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8625,50 +8625,58 @@ void md_cluster_stop(struct mddev *mddev)
> put_cluster_ops(mddev);
> }
>
> -static int is_mddev_idle(struct mddev *mddev, int init)
> +static bool is_rdev_holder_idle(struct md_rdev *rdev, bool init)
> {
> + unsigned long last_events = rdev->last_events;
> +
> + if (!bdev_is_partition(rdev->bdev))
> + return true;
Will the compiler generate code, that the assignment happens after this
condition?
> +
> + /*
> + * If rdev is partition, and user doesn't issue IO to the array, the
> + * array is still not idle if user issues IO to other partitions.
> + */
> + rdev->last_events = part_stat_read_accum(rdev->bdev->bd_disk->part0,
> + sectors) -
> + part_stat_read_accum(rdev->bdev, sectors);
> +
> + if (!init && rdev->last_events > last_events)
> + return false;
> +
> + return true;
Could be one return statement, couldn’t it?
return init || rdev->last_events <= last_events;
> +}
> +
> +/*
> + * mddev is idle if following conditions are match since last check:
… *the* following condition are match*ed* …
(or are met)
> + * 1) mddev doesn't have normal IO completed;
> + * 2) mddev doesn't have inflight normal IO;
> + * 3) if any member disk is partition, and other partitions doesn't have IO
don’t
> + * completed;
> + *
> + * Noted this checking rely on IO accounting is enabled.
> + */
> +static bool is_mddev_idle(struct mddev *mddev, int init)
> +{
> + unsigned long last_events = mddev->normal_IO_events;
> + struct gendisk *disk;
> struct md_rdev *rdev;
> - int idle;
> - int curr_events;
> + bool idle = true;
>
> - idle = 1;
> - rcu_read_lock();
> - rdev_for_each_rcu(rdev, mddev) {
> - struct gendisk *disk = rdev->bdev->bd_disk;
> + disk = mddev_is_dm(mddev) ? mddev->dm_gendisk : mddev->gendisk;
> + if (!disk)
> + return true;
>
> - if (!init && !blk_queue_io_stat(disk->queue))
> - continue;
> + mddev->normal_IO_events = part_stat_read_accum(disk->part0, sectors);
> + if (!init && (mddev->normal_IO_events > last_events ||
> + bdev_count_inflight(disk->part0)))
> + idle = false;
>
> - curr_events = (int)part_stat_read_accum(disk->part0, sectors) -
> - atomic_read(&disk->sync_io);
> - /* sync IO will cause sync_io to increase before the disk_stats
> - * as sync_io is counted when a request starts, and
> - * disk_stats is counted when it completes.
> - * So resync activity will cause curr_events to be smaller than
> - * when there was no such activity.
> - * non-sync IO will cause disk_stat to increase without
> - * increasing sync_io so curr_events will (eventually)
> - * be larger than it was before. Once it becomes
> - * substantially larger, the test below will cause
> - * the array to appear non-idle, and resync will slow
> - * down.
> - * If there is a lot of outstanding resync activity when
> - * we set last_event to curr_events, then all that activity
> - * completing might cause the array to appear non-idle
> - * and resync will be slowed down even though there might
> - * not have been non-resync activity. This will only
> - * happen once though. 'last_events' will soon reflect
> - * the state where there is little or no outstanding
> - * resync requests, and further resync activity will
> - * always make curr_events less than last_events.
> - *
> - */
> - if (init || curr_events - rdev->last_events > 64) {
> - rdev->last_events = curr_events;
> - idle = 0;
> - }
> - }
> + rcu_read_lock();
> + rdev_for_each_rcu(rdev, mddev)
> + if (!is_rdev_holder_idle(rdev, init))
> + idle = false;
> rcu_read_unlock();
> +
> return idle;
> }
>
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index b57842188f18..da3fd514d20c 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -132,7 +132,7 @@ struct md_rdev {
>
> sector_t sectors; /* Device size (in 512bytes sectors) */
> struct mddev *mddev; /* RAID array if running */
> - int last_events; /* IO event timestamp */
> + unsigned long last_events; /* IO event timestamp */
Please mention in the commit message, why the type is changed.
>
> /*
> * If meta_bdev is non-NULL, it means that a separate device is
> @@ -520,6 +520,7 @@ struct mddev {
> * adding a spare
> */
>
> + unsigned long normal_IO_events; /* IO event timestamp */
Make everything lower case?
> atomic_t recovery_active; /* blocks scheduled, but not written */
> wait_queue_head_t recovery_wait;
> sector_t recovery_cp;
Kind regards,
Paul
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