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

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Date:   Tue, 18 May 2021 22:12:42 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     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>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>,
        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, 2021-05-19 at 09:33 +0800, Huang Ying wrote:

> To test the patch, we used pmbench memory accessing benchmark with
> working-set larger than available memory on a 2-socket Intel server
> with a NVMe SSD as swap device.  Test results shows that the pmbench
> score increases up to 21.8% with the decreased size of swap cache and
> swapin throughput.

Nice!

> +++ 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);
> +		}

That's quite the if condition!

Would it make sense to move some of the tests, as well
as the trylock and unlock into try_to_free_idle_swapcache()
itself?

Especially considering that page_mapped is already tested
in that function, too...

>  		put_page(old_page);
>  	}



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