linux-kernel - Re: [PATCH 1/7] mm: Use pagevec_lookup in shmem_unlock

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Message-ID: <20200821155351.GD3432@quack2.suse.cz>
Date:   Fri, 21 Aug 2020 17:53:51 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] mm: Use pagevec_lookup in shmem_unlock_mapping

On Wed 19-08-20 16:05:49, Matthew Wilcox (Oracle) wrote:
> The comment shows that the reason for using find_get_entries() is now
> stale; find_get_pages() will not return 0 if it hits a consecutive run
> of swap entries, and I don't believe it has since 2011.  pagevec_lookup()
> is a simpler function to use than find_get_pages(), so use it instead.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

This looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  mm/shmem.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 271548ca20f3..a7bbc4ed9677 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -840,7 +840,6 @@ unsigned long shmem_swap_usage(struct vm_area_struct *vma)
>  void shmem_unlock_mapping(struct address_space *mapping)
>  {
>  	struct pagevec pvec;
> -	pgoff_t indices[PAGEVEC_SIZE];
>  	pgoff_t index = 0;
>  
>  	pagevec_init(&pvec);
> @@ -848,16 +847,8 @@ void shmem_unlock_mapping(struct address_space *mapping)
>  	 * Minor point, but we might as well stop if someone else SHM_LOCKs it.
>  	 */
>  	while (!mapping_unevictable(mapping)) {
> -		/*
> -		 * Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
> -		 * has finished, if it hits a row of PAGEVEC_SIZE swap entries.
> -		 */
> -		pvec.nr = find_get_entries(mapping, index,
> -					   PAGEVEC_SIZE, pvec.pages, indices);
> -		if (!pvec.nr)
> +		if (!pagevec_lookup(&pvec, mapping, &index))
>  			break;
> -		index = indices[pvec.nr - 1] + 1;
> -		pagevec_remove_exceptionals(&pvec);
>  		check_move_unevictable_pages(&pvec);
>  		pagevec_release(&pvec);
>  		cond_resched();
> -- 
> 2.28.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR