Re: [PATCH md-6.9 06/10] md/raid1: factor out read_first_rdev() from read_balance()
From: Xiao Ni
Date: Mon Feb 26 2024 - 20:42:57 EST
On Tue, Feb 27, 2024 at 9:23 AM Xiao Ni <xni@xxxxxxxxxx> wrote:
>
> On Tue, Feb 27, 2024 at 9:06 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> >
> > Hi,
> >
> > 在 2024/02/26 22:16, Xiao Ni 写道:
> > > On Thu, Feb 22, 2024 at 4:04 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> > >>
> > >> From: Yu Kuai <yukuai3@xxxxxxxxxx>
> > >>
> > >> 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@xxxxxxxxxxxxxxx>
> > >> Signed-off-by: Paul Luse <paul.e.luse@xxxxxxxxxxxxxxx>
> > >> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > >> ---
> > >> 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.
Sorry, I missed one thing. Beside the point I mentioned above, it
needs to update 'sectors' which is the the read region to 'len'
finally. It looks like the raid1_check_read_range needs to modify to
achieve this.
Regards
Xiao
>
> 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
> > >>
> > >>
> > >
> > > .
> > >
> >