linux-kernel - Re: [PATCH] mm: move idle swap cache pages to the tail of LRU after COW

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Date:   Wed, 19 May 2021 10:49:33 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...riel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH] mm: move idle swap cache pages to the tail of LRU after
 COW

On Wed, May 19, 2021 at 09:33:13AM +0800, Huang Ying wrote:
> diff --git a/mm/memory.c b/mm/memory.c
> index b83f734c4e1d..2b6847f4c03e 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3012,6 +3012,11 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
>  				munlock_vma_page(old_page);
>  			unlock_page(old_page);
>  		}
> +		if (page_copied && PageSwapCache(old_page) &&
> +		    !page_mapped(old_page) && trylock_page(old_page)) {
> +			try_to_free_idle_swapcache(old_page);
> +			unlock_page(old_page);

If there are no more swap or pte references, can we just attempt to
free the page right away, like we do during regular unmap?

		if (page_copied)
			free_swap_cache(old_page);
		put_page(old_page);