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SubjectRe: [PATCH v18 25/32] mm/mlock: remove lru_lock on TestClearPageMlocked in munlock_vma_page
On Mon, 24 Aug 2020, Alex Shi wrote:

> In the func munlock_vma_page, the page must be PageLocked as well as
> pages in split_huge_page series funcs. Thus the PageLocked is enough
> to serialize both funcs.
>
> So we could relief the TestClearPageMlocked/hpage_nr_pages which are not
> necessary under lru lock.
>
> As to another munlock func __munlock_pagevec, which no PageLocked
> protection and should remain lru protecting.
>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>

I made some comments on the mlock+munlock situation last week:
I won't review this 24/32 and 25/32 now, but will take a look
at your github tree tomorrow instead. Perhaps I'll find you have
already done the fixes, perhaps I'll find you have merged these back
into earlier patches. And I won't be reviewing beyond this point:
this is enough for now, I think.

Hugh

> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> ---
> mm/mlock.c | 41 +++++++++++++++--------------------------
> 1 file changed, 15 insertions(+), 26 deletions(-)
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 0448409184e3..46a05e6ec5ba 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -69,9 +69,9 @@ void clear_page_mlock(struct page *page)
> *
> * See __pagevec_lru_add_fn for more explanation.
> */
> - if (!isolate_lru_page(page)) {
> + if (!isolate_lru_page(page))
> putback_lru_page(page);
> - } else {
> + else {
> /*
> * We lost the race. the page already moved to evictable list.
> */
> @@ -178,7 +178,6 @@ static void __munlock_isolation_failed(struct page *page)
> unsigned int munlock_vma_page(struct page *page)
> {
> int nr_pages;
> - struct lruvec *lruvec;
>
> /* For try_to_munlock() and to serialize with page migration */
> BUG_ON(!PageLocked(page));
> @@ -186,37 +185,22 @@ unsigned int munlock_vma_page(struct page *page)
> VM_BUG_ON_PAGE(PageTail(page), page);
>
> /*
> - * Serialize split tail pages in __split_huge_page_tail() which
> - * might otherwise copy PageMlocked to part of the tail pages before
> - * we clear it in the head page. It also stabilizes thp_nr_pages().
> - * TestClearPageLRU can't be used here to block page isolation, since
> - * out of lock clear_page_mlock may interfer PageLRU/PageMlocked
> - * sequence, same as __pagevec_lru_add_fn, and lead the page place to
> - * wrong lru list here. So relay on PageLocked to stop lruvec change
> - * in mem_cgroup_move_account().
> + * Serialize split tail pages in __split_huge_page_tail() by
> + * lock_page(); Do TestClearPageMlocked/PageLRU sequence like
> + * clear_page_mlock().
> */
> - lruvec = lock_page_lruvec_irq(page);
> -
> - if (!TestClearPageMlocked(page)) {
> + if (!TestClearPageMlocked(page))
> /* Potentially, PTE-mapped THP: do not skip the rest PTEs */
> - nr_pages = 1;
> - goto unlock_out;
> - }
> + return 0;
>
> nr_pages = thp_nr_pages(page);
> __mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
>
> - if (__munlock_isolate_lru_page(page, lruvec, true)) {
> - unlock_page_lruvec_irq(lruvec);
> + if (!isolate_lru_page(page))
> __munlock_isolated_page(page);
> - goto out;
> - }
> - __munlock_isolation_failed(page);
> -
> -unlock_out:
> - unlock_page_lruvec_irq(lruvec);
> + else
> + __munlock_isolation_failed(page);
>
> -out:
> return nr_pages - 1;
> }
>
> @@ -305,6 +289,11 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
>
> /* block memcg change in mem_cgroup_move_account */
> lock_page_memcg(page);
> + /*
> + * Serialize split tail pages in __split_huge_page_tail() which
> + * might otherwise copy PageMlocked to part of the tail pages
> + * before we clear it in the head page.
> + */
> lruvec = relock_page_lruvec_irq(page, lruvec);
> if (TestClearPageMlocked(page)) {
> /*
> --
> 1.8.3.1
>
>

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