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Date: Mon, 7 Dec 2015 14:48:12 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v2 1/2] mm: Export nr_swap_pages
Message-ID: <20151207134812.GA20782@dhcp22.suse.cz>
References: <1449244734-25733-1-git-send-email-chris@chris-wilson.co.uk>
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To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org, "Goel, Akash" <akash.goel@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, linux-mm@kvack.org

On Fri 04-12-15 15:58:53, Chris Wilson wrote:
> Some modules, like i915.ko, use swappable objects and may try to swap
> them out under memory pressure (via the shrinker). Before doing so, they
> want to check using get_nr_swap_pages() to see if any swap space is
> available as otherwise they will waste time purging the object from the
> device without recovering any memory for the system. This requires the
> nr_swap_pages counter to be exported to the modules.

I guess it should be sufficient to change get_nr_swap_pages into a real
function and export it rather than giving the access to the counter
directly?
 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: "Goel, Akash" <akash.goel@intel.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: linux-mm@kvack.org
> ---
>  mm/swapfile.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 58877312cf6b..2d259fdb2347 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -48,6 +48,12 @@ static sector_t map_swap_entry(swp_entry_t, struct block_device**);
>  DEFINE_SPINLOCK(swap_lock);
>  static unsigned int nr_swapfiles;
>  atomic_long_t nr_swap_pages;
> +/*
> + * Some modules use swappable objects and may try to swap them out under
> + * memory pressure (via the shrinker). Before doing so, they may wish to
> + * check to see if any swap space is available.
> + */
> +EXPORT_SYMBOL_GPL(nr_swap_pages);
>  /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
>  long total_swap_pages;
>  static int least_priority;
> -- 
> 2.6.2
> 
> --
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-- 
Michal Hocko
SUSE Labs

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