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

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Message-ID: <3983c910-a02b-e67b-8c2b-7a379c3d22e1@google.com>
Date:   Tue, 10 Aug 2021 14:08:38 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Yang Shi <shy828301@...il.com>
cc:     hughd@...gle.com, ying.huang@...el.com, linmiaohe@...wei.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] Revert "mm: swap: check if swap backing device is
 congested or not"

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@...gle.com>
> Cc: "Huang, Ying" <ying.huang@...el.com>
> Cc: Miaohe Lin <linmiaohe@...wei.com>
> Signed-off-by: Yang Shi <shy828301@...il.com>

Thanks for doing these,
Acked-by: Hugh Dickins <hughd@...gle.com>
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