Re: [PATCH] mm/swap_state: update zswap LRU's protection range with the folio locked

[Chengming Zhou <chengming.zhou@linux.dev>]

On 2024/2/6 07:24, Nhat Pham wrote:
> Move the zswap LRU protection range update above the swap_read_folio()
> call, and only when a new page is allocated. This is the case where
> (z)swapin could happen, which is a signal that the zswap shrinker should
> be more conservative with its reclaiming action.
> 
> It also prevents a race, in which folio migration can clear the
> memcg_data of the now unlocked folio, resulting in a warning in the
> inlined folio_lruvec() call.
> 
> Reported-by: syzbot+17a611d10af7d18a7092@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/000000000000ae47f90610803260@google.com/
> Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure")
> Signed-off-by: Nhat Pham <nphamcs@gmail.com>

LGTM, thanks!

Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>

> ---
>  mm/swap_state.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index e671266ad772..7255c01a1e4e 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -680,9 +680,10 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
>  	/* The page was likely read above, so no need for plugging here */
>  	folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
>  					&page_allocated, false);
> -	if (unlikely(page_allocated))
> +	if (unlikely(page_allocated)) {
> +		zswap_folio_swapin(folio);
>  		swap_read_folio(folio, false, NULL);
> -	zswap_folio_swapin(folio);
> +	}
>  	return folio;
>  }
>  
> @@ -855,9 +856,10 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
>  	/* The folio was likely read above, so no need for plugging here */
>  	folio = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx,
>  					&page_allocated, false);
> -	if (unlikely(page_allocated))
> +	if (unlikely(page_allocated)) {
> +		zswap_folio_swapin(folio);
>  		swap_read_folio(folio, false, NULL);
> -	zswap_folio_swapin(folio);
> +	}
>  	return folio;
>  }
>  
> 
> base-commit: 91f3daa1765ee4e0c89987dc25f72c40f07af34d