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SubjectRe: [PATCH 5/5] mlock: fix unevictable_pgs event counts on THP
On Sun, Aug 30, 2020 at 2:09 PM Hugh Dickins <hughd@google.com> wrote:
>
> 5.8 commit 5d91f31faf8e ("mm: swap: fix vmstats for huge page") has
> established that vm_events should count every subpage of a THP,
> including unevictable_pgs_culled and unevictable_pgs_rescued; but
> lru_cache_add_inactive_or_unevictable() was not doing so for
> unevictable_pgs_mlocked, and mm/mlock.c was not doing so for
> unevictable_pgs mlocked, munlocked, cleared and stranded.
>
> Fix them; but THPs don't go the pagevec way in mlock.c,
> so no fixes needed on that path.
>
> Fixes: 5d91f31faf8e ("mm: swap: fix vmstats for huge page")
> Signed-off-by: Hugh Dickins <hughd@google.com>

Acked-by: Yang Shi <shy828301@gmail.com>

> ---
> I've only checked UNEVICTABLEs: there may be more inconsistencies left.
> The check_move_unevictable_pages() patch brought me to this one, but
> this is more important because mlock works on all THPs, without needing
> special testing "force". But, it's still just monotonically increasing
> event counts, so not all that important.
>
> mm/mlock.c | 24 +++++++++++++++---------
> mm/swap.c | 6 +++---
> 2 files changed, 18 insertions(+), 12 deletions(-)
>
> --- 5.9-rc2/mm/mlock.c 2020-08-16 17:32:50.665507048 -0700
> +++ linux/mm/mlock.c 2020-08-28 17:42:07.975278411 -0700
> @@ -58,11 +58,14 @@ EXPORT_SYMBOL(can_do_mlock);
> */
> void clear_page_mlock(struct page *page)
> {
> + int nr_pages;
> +
> if (!TestClearPageMlocked(page))
> return;
>
> - mod_zone_page_state(page_zone(page), NR_MLOCK, -thp_nr_pages(page));
> - count_vm_event(UNEVICTABLE_PGCLEARED);
> + nr_pages = thp_nr_pages(page);
> + mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
> + count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
> /*
> * The previous TestClearPageMlocked() corresponds to the smp_mb()
> * in __pagevec_lru_add_fn().
> @@ -76,7 +79,7 @@ void clear_page_mlock(struct page *page)
> * We lost the race. the page already moved to evictable list.
> */
> if (PageUnevictable(page))
> - count_vm_event(UNEVICTABLE_PGSTRANDED);
> + count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
> }
> }
>
> @@ -93,9 +96,10 @@ void mlock_vma_page(struct page *page)
> VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);
>
> if (!TestSetPageMlocked(page)) {
> - mod_zone_page_state(page_zone(page), NR_MLOCK,
> - thp_nr_pages(page));
> - count_vm_event(UNEVICTABLE_PGMLOCKED);
> + int nr_pages = thp_nr_pages(page);
> +
> + mod_zone_page_state(page_zone(page), NR_MLOCK, nr_pages);
> + count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
> if (!isolate_lru_page(page))
> putback_lru_page(page);
> }
> @@ -138,7 +142,7 @@ static void __munlock_isolated_page(stru
>
> /* Did try_to_unlock() succeed or punt? */
> if (!PageMlocked(page))
> - count_vm_event(UNEVICTABLE_PGMUNLOCKED);
> + count_vm_events(UNEVICTABLE_PGMUNLOCKED, thp_nr_pages(page));
>
> putback_lru_page(page);
> }
> @@ -154,10 +158,12 @@ static void __munlock_isolated_page(stru
> */
> static void __munlock_isolation_failed(struct page *page)
> {
> + int nr_pages = thp_nr_pages(page);
> +
> if (PageUnevictable(page))
> - __count_vm_event(UNEVICTABLE_PGSTRANDED);
> + __count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
> else
> - __count_vm_event(UNEVICTABLE_PGMUNLOCKED);
> + __count_vm_events(UNEVICTABLE_PGMUNLOCKED, nr_pages);
> }
>
> /**
> --- 5.9-rc2/mm/swap.c 2020-08-16 17:32:50.709507284 -0700
> +++ linux/mm/swap.c 2020-08-28 17:42:07.975278411 -0700
> @@ -494,14 +494,14 @@ void lru_cache_add_inactive_or_unevictab
>
> unevictable = (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED;
> if (unlikely(unevictable) && !TestSetPageMlocked(page)) {
> + int nr_pages = thp_nr_pages(page);
> /*
> * We use the irq-unsafe __mod_zone_page_stat because this
> * counter is not modified from interrupt context, and the pte
> * lock is held(spinlock), which implies preemption disabled.
> */
> - __mod_zone_page_state(page_zone(page), NR_MLOCK,
> - thp_nr_pages(page));
> - count_vm_event(UNEVICTABLE_PGMLOCKED);
> + __mod_zone_page_state(page_zone(page), NR_MLOCK, nr_pages);
> + count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
> }
> lru_cache_add(page);
> }
>

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