Re: [PATCH] fs: annotate refault stalls from bdev_read_page

[Shakeel Butt <shakeelb@google.com>]

On Wed, Oct 9, 2019 at 2:19 PM Minchan Kim <minchan@kernel.org> wrote:
>
> From: Minchan Kim <minchan@google.com>
>
> If block device supports rw_page operation, it doesn't submit bio
> so annotation in submit_bio for refault stall doesn't work.
> It happens with zram in android, especially swap read path which
> could consume CPU cycle for decompress.

What about zswap? Do we need the same in zswap_frontswap_load()?

>
> Annotate bdev_read_page() to account the synchronous IO overhead
> to prevent underreport memory pressure.
>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Minchan Kim <minchan@google.com>
> ---
>  fs/block_dev.c | 13 +++++++++++++
>  mm/memory.c    |  1 +
>  2 files changed, 14 insertions(+)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 9c073dbdc1b0..82ca28eb9a57 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -26,6 +26,7 @@
>  #include <linux/writeback.h>
>  #include <linux/mpage.h>
>  #include <linux/mount.h>
> +#include <linux/psi.h>
>  #include <linux/pseudo_fs.h>
>  #include <linux/uio.h>
>  #include <linux/namei.h>
> @@ -701,6 +702,8 @@ int bdev_read_page(struct block_device *bdev, sector_t sector,
>  {
>         const struct block_device_operations *ops = bdev->bd_disk->fops;
>         int result = -EOPNOTSUPP;
> +       unsigned long pflags;
> +       bool workingset_read;
>
>         if (!ops->rw_page || bdev_get_integrity(bdev))
>                 return result;
> @@ -708,9 +711,19 @@ int bdev_read_page(struct block_device *bdev, sector_t sector,
>         result = blk_queue_enter(bdev->bd_queue, 0);
>         if (result)
>                 return result;
> +
> +       workingset_read = PageWorkingset(page);
> +       if (workingset_read)
> +               psi_memstall_enter(&pflags);
> +
>         result = ops->rw_page(bdev, sector + get_start_sect(bdev), page,
>                               REQ_OP_READ);
> +
> +       if (workingset_read)
> +               psi_memstall_leave(&pflags);
> +
>         blk_queue_exit(bdev->bd_queue);
> +
>         return result;
>  }
>  EXPORT_SYMBOL_GPL(bdev_read_page);
> diff --git a/mm/memory.c b/mm/memory.c
> index 06935826d71e..6357d5a0a2a5 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2801,6 +2801,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>                         if (page) {
>                                 __SetPageLocked(page);
>                                 __SetPageSwapBacked(page);
> +                               SetPageWorkingset(page);
>                                 set_page_private(page, entry.val);
>                                 lru_cache_add_anon(page);
>                                 swap_readpage(page, true);
> --
> 2.23.0.581.g78d2f28ef7-goog
>