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Message-ID: <3be3dacd-1f45-468f-a363-b9d3a10aeb89@redhat.com>
Date: Tue, 30 Jul 2024 17:14:33 +0200
From: David Hildenbrand <david@...hat.com>
To: Usama Arif <usamaarif642@...il.com>, akpm@...ux-foundation.org,
linux-mm@...ck.org
Cc: hannes@...xchg.org, riel@...riel.com, shakeel.butt@...ux.dev,
roman.gushchin@...ux.dev, yuzhao@...gle.com, baohua@...nel.org,
ryan.roberts@....com, rppt@...nel.org, willy@...radead.org,
cerasuolodomenico@...il.com, corbet@....net, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, kernel-team@...a.com,
Shuang Zhai <zhais@...gle.com>
Subject: Re: [PATCH 3/6] mm: free zapped tail pages when splitting isolated
thp
On 30.07.24 14:46, Usama Arif wrote:
> From: Yu Zhao <yuzhao@...gle.com>
>
> If a tail page has only two references left, one inherited from the
> isolation of its head and the other from lru_add_page_tail() which we
> are about to drop, it means this tail page was concurrently zapped.
> Then we can safely free it and save page reclaim or migration the
> trouble of trying it.
>
> Signed-off-by: Yu Zhao <yuzhao@...gle.com>
> Tested-by: Shuang Zhai <zhais@...gle.com>
> Signed-off-by: Usama Arif <usamaarif642@...il.com>
> ---
> mm/huge_memory.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 0167dc27e365..76a3b6a2b796 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2923,6 +2923,8 @@ static void __split_huge_page(struct page *page, struct list_head *list,
> unsigned int new_nr = 1 << new_order;
> int order = folio_order(folio);
> unsigned int nr = 1 << order;
> + LIST_HEAD(pages_to_free);
> + int nr_pages_to_free = 0;
>
> /* complete memcg works before add pages to LRU */
> split_page_memcg(head, order, new_order);
> @@ -3007,6 +3009,24 @@ static void __split_huge_page(struct page *page, struct list_head *list,
> if (subpage == page)
> continue;
> folio_unlock(new_folio);
> + /*
> + * If a tail page has only two references left, one inherited
> + * from the isolation of its head and the other from
> + * lru_add_page_tail() which we are about to drop, it means this
> + * tail page was concurrently zapped. Then we can safely free it
> + * and save page reclaim or migration the trouble of trying it.
> + */
> + if (list && page_ref_freeze(subpage, 2)) {
> + VM_BUG_ON_PAGE(PageLRU(subpage), subpage);
> + VM_BUG_ON_PAGE(PageCompound(subpage), subpage);
> + VM_BUG_ON_PAGE(page_mapped(subpage), subpage);
> +
No VM_BUG_*, VM_WARN is good enough.
> + ClearPageActive(subpage);
> + ClearPageUnevictable(subpage);
> + list_move(&subpage->lru, &pages_to_free);
Most checks here should operate on new_folio instead of subpage.
--
Cheers,
David / dhildenb
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