On Jun 6, 2012 6:55 AM, "Sasha Levin" <levinsasha928@xxxxxxxxx> wrote:
>
> Split frontswap_shrink to eliminate the locking issues in the original code.
Can you describe the locking issue please?
>
> Signed-off-by: Sasha Levin <levinsasha928@xxxxxxxxx>
> ---
> mm/frontswap.c | 36 +++++++++++++++++++++---------------
> 1 files changed, 21 insertions(+), 15 deletions(-)
>
> diff --git a/mm/frontswap.c b/mm/frontswap.c
> index a9b76cb..618ef91 100644
> --- a/mm/frontswap.c
> +++ b/mm/frontswap.c
> @@ -244,6 +244,24 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
> return ret;
> }
>
> +static int __frontswap_shrink(unsigned long target_pages,
> + unsigned long *pages_to_unuse,
> + int *type)
> +{
> + unsigned long total_pages = 0, total_pages_to_unuse;
> +
> + lockdep_assert_held(&swap_lock);
> +
> + total_pages = __frontswap_curr_pages();
> + if (total_pages <= target_pages) {
> + /* Nothing to do */
> + *pages_to_unuse = 0;
> + return 0;
> + }
> + total_pages_to_unuse = total_pages - target_pages;
> + return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
> +}
> +
> /*
> * Frontswap, like a true swap device, may unnecessarily retain pages
> * under certain circumstances; "shrink" frontswap is essentially a
> @@ -254,10 +272,8 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
> */
> void frontswap_shrink(unsigned long target_pages)
> {
> - unsigned long total_pages = 0, total_pages_to_unuse;
> unsigned long pages_to_unuse = 0;
> int type, ret;
> - bool locked = false;
>
> /*
> * we don't want to hold swap_lock while doing a very
> @@ -265,20 +281,10 @@ void frontswap_shrink(unsigned long target_pages)
> * so restart scan from swap_list.head each time
> */
> spin_lock(&swap_lock);
> - locked = true;
> - total_pages = __frontswap_curr_pages();
> - if (total_pages <= target_pages)
> - goto out;
> - total_pages_to_unuse = total_pages - target_pages;
> - ret = __frontswap_unuse_pages(total_pages_to_unuse, &pages_to_unuse, &type);
> - if (ret < 0)
> - goto out;
> - locked = false;
> + ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
> spin_unlock(&swap_lock);
> - try_to_unuse(type, true, pages_to_unuse);
> -out:
> - if (locked)
> - spin_unlock(&swap_lock);
> + if (ret == 0 && pages_to_unuse)
> + try_to_unuse(type, true, pages_to_unuse);
> return;
> }
> EXPORT_SYMBOL(frontswap_shrink);
> --
> 1.7.8.6
>
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