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From:   Song Liu <song@kernel.org>
Date:   Tue, 10 Mar 2020 14:40:07 -0700
Message-ID: <CAPhsuW6xJeX3=0j69_hdaUnYXPm7VeaXHB06JM=fRZsxPweQng@mail.gmail.com>
Subject: Re: [PATCH] block: keep bdi->io_pages in sync with max_sectors_kb for
 stacked devices
To:     Bob Liu <bob.liu@oracle.com>
Cc:     Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        open list <linux-kernel@vger.kernel.org>,
        linux-raid <linux-raid@vger.kernel.org>,
        Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
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On Mon, Mar 2, 2020 at 4:16 AM Bob Liu <bob.liu@oracle.com> wrote:
>
> On 2/28/20 10:51 PM, Konstantin Khlebnikov wrote:
> > Field bdi->io_pages added in commit 9491ae4aade6 ("mm: don't cap request
> > size based on read-ahead setting") removes unneeded split of read requests.
> >
> > Stacked drivers do not call blk_queue_max_hw_sectors(). Instead they setup
> > limits of their devices by blk_set_stacking_limits() + disk_stack_limits().
> > Field bio->io_pages stays zero until user set max_sectors_kb via sysfs.
> >
> > This patch updates io_pages after merging limits in disk_stack_limits().
> >
> > Commit c6d6e9b0f6b4 ("dm: do not allow readahead to limit IO size") fixed
> > the same problem for device-mapper devices, this one fixes MD RAIDs.
> >
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > ---
> >  block/blk-settings.c |    2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/block/blk-settings.c b/block/blk-settings.c
> > index c8eda2e7b91e..66c45fd79545 100644
> > --- a/block/blk-settings.c
> > +++ b/block/blk-settings.c
> > @@ -664,6 +664,8 @@ void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
> >               printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
> >                      top, bottom);
> >       }
> > +
> > +     t->backing_dev_info->io_pages = t->limits.max_sectors >> (PAGE_SHIFT-9);
> >  }
> >  EXPORT_SYMBOL(disk_stack_limits);
> >
> >
>
> Nitpick.. (PAGE_SHIFT - 9)
> Reviewed-by: Bob Liu <bob.liu@oracle.com>

Thanks for the fix. I fixed it based on the comments and applied it to md-next.

Jens, I picked the patch to md-next because md is the only user of
disk_stack_limits().

Please let me know if you prefer routing it via the block tree.

Thanks,
Song