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SubjectRe: [PATCH 6/9] ksm: mem cgroup charge swapin copy
On Tue, 24 Nov 2009 16:51:13 +0000 (GMT)
Hugh Dickins <hugh.dickins@tiscali.co.uk> wrote:
> But ksm swapping does require one small change in mem cgroup handling.
> When do_swap_page()'s call to ksm_might_need_to_copy() does indeed
> substitute a duplicate page to accommodate a different anon_vma (or a
> different index), that page escaped mem cgroup accounting, because of
> the !PageSwapCache check in mem_cgroup_try_charge_swapin().
>
> That was returning success without charging, on the assumption that
> pte_same() would fail after, which is not the case here. Originally I
> proposed that success, so that an unshrinkable mem cgroup at its limit
> would not fail unnecessarily; but that's a minor point, and there are
> plenty of other places where we may fail an overallocation which might
> later prove unnecessary. So just go ahead and do what all the other
> exceptions do: proceed to charge current mm.
>
> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>

Ok. Maybe commit_charge will work enough. (I hope so.)

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

BTW, I'm happy if you adds "How to test" documenation to
Documentation/vm/ksm.txt or to share some test programs.

1. Map anonymous pages + madvise(MADV_MERGEABLE)
2. "echo 1 > /sys/kernel/mm/ksm/run"
is enough ?

Thanks,
-Kame

> ---
>
> mm/memcontrol.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> --- ksm5/mm/memcontrol.c 2009-11-14 10:17:02.000000000 +0000
> +++ ksm6/mm/memcontrol.c 2009-11-22 20:40:37.000000000 +0000
> @@ -1862,11 +1862,12 @@ int mem_cgroup_try_charge_swapin(struct
> goto charge_cur_mm;
> /*
> * A racing thread's fault, or swapoff, may have already updated
> - * the pte, and even removed page from swap cache: return success
> - * to go on to do_swap_page()'s pte_same() test, which should fail.
> + * 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))
> - return 0;
> + goto charge_cur_mm;
> mem = try_get_mem_cgroup_from_swapcache(page);
> if (!mem)
> goto charge_cur_mm;
> --
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