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Date: Tue, 27 Feb 2024 10:04:06 +0800
From: Xiao Ni <xni@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: paul.e.luse@...ux.intel.com, song@...nel.org, neilb@...e.com, shli@...com,
linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org, yukuai3@...wei.com,
yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH md-6.9 09/10] md/raid1: factor out the code to manage
sequential IO
On Thu, Feb 22, 2024 at 4:05 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@...wei.com>
>
> There is no functional change for now, make read_balance() cleaner and
> prepare to fix problems and refactor the handler of sequential IO.
>
> Co-developed-by: Paul Luse <paul.e.luse@...ux.intel.com>
> Signed-off-by: Paul Luse <paul.e.luse@...ux.intel.com>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> drivers/md/raid1.c | 71 +++++++++++++++++++++++++---------------------
> 1 file changed, 38 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 4694e0e71e36..223ef8d06f67 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -705,6 +705,31 @@ static int choose_slow_rdev(struct r1conf *conf, struct r1bio *r1_bio,
> return bb_disk;
> }
>
> +static bool is_sequential(struct r1conf *conf, int disk, struct r1bio *r1_bio)
> +{
> + /* TODO: address issues with this check and concurrency. */
> + return conf->mirrors[disk].next_seq_sect == r1_bio->sector ||
> + conf->mirrors[disk].head_position == r1_bio->sector;
> +}
> +
> +/*
> + * If buffered sequential IO size exceeds optimal iosize, check if there is idle
> + * disk. If yes, choose the idle disk.
> + */
> +static bool should_choose_next(struct r1conf *conf, int disk)
> +{
> + struct raid1_info *mirror = &conf->mirrors[disk];
> + int opt_iosize;
> +
> + if (!test_bit(Nonrot, &mirror->rdev->flags))
> + return false;
> +
> + opt_iosize = bdev_io_opt(mirror->rdev->bdev) >> 9;
> + return opt_iosize > 0 && mirror->seq_start != MaxSector &&
> + mirror->next_seq_sect > opt_iosize &&
> + mirror->next_seq_sect - opt_iosize >= mirror->seq_start;
> +}
> +
> /*
> * This routine returns the disk from which the requested read should
> * be done. There is a per-array 'next expected sequential IO' sector
> @@ -767,42 +792,22 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> pending = atomic_read(&rdev->nr_pending);
> dist = abs(this_sector - conf->mirrors[disk].head_position);
> /* Don't change to another disk for sequential reads */
> - if (conf->mirrors[disk].next_seq_sect == this_sector
> - || dist == 0) {
> - int opt_iosize = bdev_io_opt(rdev->bdev) >> 9;
> - struct raid1_info *mirror = &conf->mirrors[disk];
> -
> - /*
> - * If buffered sequential IO size exceeds optimal
> - * iosize, check if there is idle disk. If yes, choose
> - * the idle disk. read_balance could already choose an
> - * idle disk before noticing it's a sequential IO in
> - * this disk. This doesn't matter because this disk
> - * will idle, next time it will be utilized after the
> - * first disk has IO size exceeds optimal iosize. In
> - * this way, iosize of the first disk will be optimal
> - * iosize at least. iosize of the second disk might be
> - * small, but not a big deal since when the second disk
> - * starts IO, the first disk is likely still busy.
> - */
> - if (test_bit(Nonrot, &rdev->flags) && opt_iosize > 0 &&
> - mirror->seq_start != MaxSector &&
> - mirror->next_seq_sect > opt_iosize &&
> - mirror->next_seq_sect - opt_iosize >=
> - mirror->seq_start) {
> - /*
> - * Add 'pending' to avoid choosing this disk if
> - * there is other idle disk.
> - * Set 'dist' to 0, so that if there is no other
> - * idle disk and all disks are rotational, this
> - * disk will still be chosen.
> - */
> - pending++;
> - dist = 0;
> - } else {
> + if (is_sequential(conf, disk, r1_bio)) {
> + if (!should_choose_next(conf, disk)) {
> best_disk = disk;
> break;
> }
> +
> + /*
> + * Add 'pending' to avoid choosing this disk if there is
> + * other idle disk.
> + */
> + pending++;
> + /*
> + * Set 'dist' to 0, so that if there is no other idle
> + * disk, this disk will still be chosen.
> + */
> + dist = 0;
> }
>
> if (min_pending > pending) {
> --
> 2.39.2
>
>
Hi
This patch looks good to me.
Reviewed-by: Xiao Ni <xni@...hat.com>
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