Re: [PATCH 3/3] Revert "mm: swap: check if swap backing device is congested or not"

[Hugh Dickins]

On Tue, 10 Aug 2021, Yang Shi wrote:

> Due to the change about how block layer detects congestion the
> justification of commit 8fd2e0b505d1 ("mm: swap: check if swap backing device
> is congested or not") doesn't stand anymore, so the commit could be just
> reverted in order to solve the race reported by commit 2efa33fc7f6e ("mm/shmem:
> fix shmem_swapin() race with swapoff"). The fix was reverted by the
> previous patch.
> 
> Suggested-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>

Thanks for doing these,
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
to all three.

I guess 1/3 will vanish now, since what it's reverting has not yet gone
forward to Linus: it would have been nice for 2/3 to have mentioned that
what it's reverting is kindof buggy: but then you'd have to explain the
"kindof", and that takes more words than it's worth - maybe a lore Link
to the discussion?

But you've done the work that I've not yet got around to:
so thank you, and ignore my gripes.

Hugh

> ---
>  mm/swap_state.c | 7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 1a29b4f98208..8d4104242100 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -628,13 +628,6 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
>  	if (!mask)
>  		goto skip;
>  
> -	/* Test swap type to make sure the dereference is safe */
> -	if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) {
> -		struct inode *inode = si->swap_file->f_mapping->host;
> -		if (inode_read_congested(inode))
> -			goto skip;
> -	}
> -
>  	do_poll = false;
>  	/* Read a page_cluster sized and aligned cluster around offset. */
>  	start_offset = offset & ~mask;
> -- 
> 2.26.2