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

[Rik van Riel]

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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