Re: [PATCH 06/13] mm/munlock: maintain page->mlock_count while unevictable

Vlastimil Babka
2022-02-11T18:07:23Z

On 2/6/22 22:40, Hugh Dickins wrote:
> @@ -72,19 +91,40 @@ void mlock_page(struct page *page)
> */
> void munlock_page(struct page *page)
> {
> + struct lruvec *lruvec;
> + int nr_pages = thp_nr_pages(page);
> +
> VM_BUG_ON_PAGE(PageTail(page), page);
>
> + lock_page_memcg(page);

Hm this (and unlock_page_memcg() below) didn't catch my attention until I
see patch 10/13 removes it again. It also AFAICS wasn't present in the code
removed by patch 1. Am I missing something or it wasn't necessary to add it
in the first place?

> + lruvec = folio_lruvec_lock_irq(page_folio(page));
> + if (PageLRU(page) && PageUnevictable(page)) {
> + /* Then mlock_count is maintained, but might undercount */
> + if (page->mlock_count)
> + page->mlock_count--;
> + if (page->mlock_count)
> + goto out;
> + }
> + /* else assume that was the last mlock: reclaim will fix it if not */
> +
> if (TestClearPageMlocked(page)) {
> - int nr_pages = thp_nr_pages(page);
> -
> - mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
> - if (!isolate_lru_page(page)) {
> - putback_lru_page(page);
> - count_vm_events(UNEVICTABLE_PGMUNLOCKED, nr_pages);
> - } else if (PageUnevictable(page)) {
> - count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
> - }
> + __mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
> + if (PageLRU(page) || !PageUnevictable(page))
> + __count_vm_events(UNEVICTABLE_PGMUNLOCKED, nr_pages);
> + else
> + __count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
> + }
> +
> + /* page_evictable() has to be checked *after* clearing Mlocked */
> + if (PageLRU(page) && PageUnevictable(page) && page_evictable(page)) {
> + del_page_from_lru_list(page, lruvec);
> + ClearPageUnevictable(page);
> + add_page_to_lru_list(page, lruvec);
> + __count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
> }
> +out:
> + unlock_page_lruvec_irq(lruvec);
> + unlock_page_memcg(page);
> }
>
> /*