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Message-ID: <CALTww2_q3XG5HFCYm3Wp7=fjM04cdWZy34R6MsDVLz-82iO88Q@mail.gmail.com>
Date: Tue, 27 Feb 2024 09:23:22 +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, yi.zhang@...wei.com,
yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH md-6.9 06/10] md/raid1: factor out read_first_rdev() from read_balance()
On Tue, Feb 27, 2024 at 9:06 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2024/02/26 22:16, Xiao Ni 写道:
> > On Thu, Feb 22, 2024 at 4:04 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
> >>
> >> From: Yu Kuai <yukuai3@...wei.com>
> >>
> >> read_balance() is hard to understand because there are too many status
> >> and branches, and it's overlong.
> >>
> >> This patch factor out the case to read the first rdev from
> >> read_balance(), there are no functional changes.
> >>
> >> 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 | 63 +++++++++++++++++++++++++++++++++-------------
> >> 1 file changed, 46 insertions(+), 17 deletions(-)
> >>
> >> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> >> index 8089c569e84f..08c45ca55a7e 100644
> >> --- a/drivers/md/raid1.c
> >> +++ b/drivers/md/raid1.c
> >> @@ -579,6 +579,47 @@ static sector_t align_to_barrier_unit_end(sector_t start_sector,
> >> return len;
> >> }
> >>
> >> +static void update_read_sectors(struct r1conf *conf, int disk,
> >> + sector_t this_sector, int len)
> >> +{
> >> + struct raid1_info *info = &conf->mirrors[disk];
> >> +
> >> + atomic_inc(&info->rdev->nr_pending);
> >> + if (info->next_seq_sect != this_sector)
> >> + info->seq_start = this_sector;
> >> + info->next_seq_sect = this_sector + len;
> >> +}
> >> +
> >> +static int choose_first_rdev(struct r1conf *conf, struct r1bio *r1_bio,
> >> + int *max_sectors)
> >> +{
> >> + sector_t this_sector = r1_bio->sector;
> >> + int len = r1_bio->sectors;
> >> + int disk;
> >> +
> >> + for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
> >> + struct md_rdev *rdev;
> >> + int read_len;
> >> +
> >> + if (r1_bio->bios[disk] == IO_BLOCKED)
> >> + continue;
> >> +
> >> + rdev = conf->mirrors[disk].rdev;
> >> + if (!rdev || test_bit(Faulty, &rdev->flags))
> >> + continue;
> >> +
> >> + /* choose the first disk even if it has some bad blocks. */
> >> + read_len = raid1_check_read_range(rdev, this_sector, &len);
> >> + if (read_len > 0) {
> >> + update_read_sectors(conf, disk, this_sector, read_len);
> >> + *max_sectors = read_len;
> >> + return disk;
> >> + }
> >
> > Hi Kuai
> >
> > It needs to update max_sectors even if the bad block starts before
> > this_sector. Because it can't read more than bad_blocks from other
> > member disks. If it reads more data than bad blocks, it will cause
> > data corruption. One rule here is read from the primary disk (the
> > first readable disk) if it has no bad block and read the
> > badblock-data-length data from other disks.
>
> Noted that raid1_check_read_range() will return readable length from
> this rdev, hence if bad block starts before this_sector, 0 is returned,
> and 'len' is updated to the length of badblocks(if not exceed read
> range), and following iteration will find the first disk to read updated
> 'len' data and update max_sectors.
Hi Kuai
The problem is that choose_first_rdev doesn't return 'len' from
max_sectors when bad blocks start before this_sector. In the following
iteration, it can't read more than 'len' from other disks to avoid
data corruption. I haven't read all the patches. To this patch, it
resets best_good_sectors to sectors when it encounters a good member
disk without bad blocks.
Regards
Xiao
>
> Thanks,
> Kuai
>
> >
> > Best Regards
> > Xiao
> >
> >> + }
> >> +
> >> + return -1;
> >> +}
> >> +
> >> /*
> >> * This routine returns the disk from which the requested read should
> >> * be done. There is a per-array 'next expected sequential IO' sector
> >> @@ -603,7 +644,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> >> sector_t best_dist;
> >> unsigned int min_pending;
> >> struct md_rdev *rdev;
> >> - int choose_first;
> >>
> >> retry:
> >> sectors = r1_bio->sectors;
> >> @@ -613,10 +653,11 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> >> best_pending_disk = -1;
> >> min_pending = UINT_MAX;
> >> best_good_sectors = 0;
> >> - choose_first = raid1_should_read_first(conf->mddev, this_sector,
> >> - sectors);
> >> clear_bit(R1BIO_FailFast, &r1_bio->state);
> >>
> >> + if (raid1_should_read_first(conf->mddev, this_sector, sectors))
> >> + return choose_first_rdev(conf, r1_bio, max_sectors);
> >> +
> >> for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
> >> sector_t dist;
> >> sector_t first_bad;
> >> @@ -662,8 +703,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> >> * bad_sectors from another device..
> >> */
> >> bad_sectors -= (this_sector - first_bad);
> >> - if (choose_first && sectors > bad_sectors)
> >> - sectors = bad_sectors;
> >> if (best_good_sectors > sectors)
> >> best_good_sectors = sectors;
> >>
> >> @@ -673,8 +712,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> >> best_good_sectors = good_sectors;
> >> best_disk = disk;
> >> }
> >> - if (choose_first)
> >> - break;
> >> }
> >> continue;
> >> } else {
> >> @@ -689,10 +726,6 @@ 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);
> >> - if (choose_first) {
> >> - best_disk = disk;
> >> - break;
> >> - }
> >> /* Don't change to another disk for sequential reads */
> >> if (conf->mirrors[disk].next_seq_sect == this_sector
> >> || dist == 0) {
> >> @@ -760,13 +793,9 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
> >> rdev = conf->mirrors[best_disk].rdev;
> >> if (!rdev)
> >> goto retry;
> >> - atomic_inc(&rdev->nr_pending);
> >> - sectors = best_good_sectors;
> >> -
> >> - if (conf->mirrors[best_disk].next_seq_sect != this_sector)
> >> - conf->mirrors[best_disk].seq_start = this_sector;
> >>
> >> - conf->mirrors[best_disk].next_seq_sect = this_sector + sectors;
> >> + sectors = best_good_sectors;
> >> + update_read_sectors(conf, disk, this_sector, sectors);
> >> }
> >> *max_sectors = sectors;
> >>
> >> --
> >> 2.39.2
> >>
> >>
> >
> > .
> >
>
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