On Thu 05-07-12 02:45:03, Johannes Weiner wrote:
> shmem knows for sure that the page is in swap cache when attempting to
> charge a page, because the cache charge entry function has a check for
> it. Only anon pages may be removed from swap cache already when
> trying to charge their swapin.
>
> Adjust the comment, though: '4969c11 mm: fix swapin race condition'
> added a stable PageSwapCache check under the page lock in the
> do_swap_page() before calling the memory controller, so it's
> unuse_pte()'s pte_same() that may fail.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Looks good
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/memcontrol.c | 22 ++++++++++++++--------
> 1 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d3701cd..9b7e256 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2751,14 +2751,6 @@ static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
> return 0;
> if (!do_swap_account)
> goto charge_cur_mm;
> - /*
> - * A racing thread's fault, or swapoff, may have already updated
> - * the pte, and even removed page from swap cache: in those cases
> - * do_swap_page()'s pte_same() test will fail; but there's also a
> - * KSM case which does need to charge the page.
> - */
> - if (!PageSwapCache(page))
> - goto charge_cur_mm;
> memcg = try_get_mem_cgroup_from_page(page);
> if (!memcg)
> goto charge_cur_mm;
> @@ -2781,6 +2773,20 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
> *memcgp = NULL;
> if (mem_cgroup_disabled())
> return 0;
> + /*
> + * A racing thread's fault, or swapoff, may have already
> + * updated the pte, and even removed page from swap cache: in
> + * those cases unuse_pte()'s pte_same() test will fail; but
> + * there's also a KSM case which does need to charge the page.
> + */
> + if (!PageSwapCache(page)) {
> + int ret;
> +
> + ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);
> + if (ret == -EINTR)
> + ret = 0;
> + return ret;
> + }
> return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);
> }
>
> --
> 1.7.7.6
>
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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