linux-kernel - Re: [PATCH 6/7] mm: free swap cache aggressively if memcg swap is full

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Date:	Fri, 11 Dec 2015 14:33:58 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] mm: free swap cache aggressively if memcg swap is
 full

On Thu, Dec 10, 2015 at 02:39:19PM +0300, Vladimir Davydov wrote:
> Swap cache pages are freed aggressively if swap is nearly full (>50%
> currently), because otherwise we are likely to stop scanning anonymous
> when we near the swap limit even if there is plenty of freeable swap
> cache pages. We should follow the same trend in case of memory cgroup,
> which has its own swap limit.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>

One note:

> @@ -5839,6 +5839,29 @@ long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg)
>  	return nr_swap_pages;
>  }
>  
> +bool mem_cgroup_swap_full(struct page *page)
> +{
> +	struct mem_cgroup *memcg;
> +
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +
> +	if (vm_swap_full())
> +		return true;
> +	if (!do_swap_account || !PageSwapCache(page))
> +		return false;

The callers establish PageSwapCache() under the page lock, which makes
sense since they only inquire about the swap state when deciding what
to do with a swapcache page at hand. So this check seems unnecessary.
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