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    SubjectRe: [PATCH] thp: reduce khugepaged freezing latency
    On Wed, Nov 09, 2011 at 01:31:07AM +0530, Srivatsa S. Bhat wrote:
    > On 11/08/2011 08:59 PM, Andrea Arcangeli wrote:
    > > Lack of set_freezable_with_signal() prevented khugepaged to be waken
    > > up (and prevented to sleep again) across the
    > > schedule_timeout_interruptible() calls after freezing() becomes
    > > true. The tight loop in khugepaged_alloc_hugepage() also missed one
    > > try_to_freeze() call in case alloc_hugepage() would repeatedly fail in
    > > turn preventing the loop to break and to reach the try_to_freeze() in
    > > the khugepaged main loop.
    > >
    > > khugepaged would still freeze just fine by trying again the next
    > > minute but it's better if it freezes immediately.
    > >
    > > Reported-by: Jiri Slaby <jslaby@suse.cz>
    > > Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
    > > ---
    > > mm/huge_memory.c | 3 ++-
    > > 1 files changed, 2 insertions(+), 1 deletions(-)
    > >
    > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    > > index 4298aba..67311d1 100644
    > > --- a/mm/huge_memory.c
    > > +++ b/mm/huge_memory.c
    > > @@ -2277,6 +2277,7 @@ static struct page *khugepaged_alloc_hugepage(void)
    > > if (!hpage) {
    > > count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
    > > khugepaged_alloc_sleep();
    > > + try_to_freeze();
    > > } else
    > > count_vm_event(THP_COLLAPSE_ALLOC);
    > > } while (unlikely(!hpage) &&
    > > @@ -2331,7 +2332,7 @@ static int khugepaged(void *none)
    > > {
    > > struct mm_slot *mm_slot;
    > >
    > > - set_freezable();
    > > + set_freezable_with_signal();
    > > set_user_nice(current, 19);
    > >
    > > /* serialize with start_khugepaged() */
    > >
    >
    > Why do we need to use both set_freezable_with_signal() and an additional
    > try_to_freeze()? Won't just using either one of them be good enough?
    > Or am I missing something here?

    set_freezable_with_signal() makes khugepaged quit and not re-enter the
    sleep, try_to_freeze is needed to get the task from freezing to
    frozen, otherwise it'll loop without getting frozen.


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