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[2003:cb:c706:4e00:31ad:5274:e21c:b59]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4281d805323sm71607225e9.41.2024.07.30.08.14.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Jul 2024 08:14:34 -0700 (PDT) Message-ID: <3be3dacd-1f45-468f-a363-b9d3a10aeb89@redhat.com> Date: Tue, 30 Jul 2024 17:14:33 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/6] mm: free zapped tail pages when splitting isolated thp To: Usama Arif , akpm@linux-foundation.org, linux-mm@kvack.org Cc: hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, yuzhao@google.com, baohua@kernel.org, ryan.roberts@arm.com, rppt@kernel.org, willy@infradead.org, cerasuolodomenico@gmail.com, corbet@lwn.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com, Shuang Zhai References: <20240730125346.1580150-1-usamaarif642@gmail.com> <20240730125346.1580150-4-usamaarif642@gmail.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 30.07.24 14:46, Usama Arif wrote: > From: Yu Zhao > > 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 > Tested-by: Shuang Zhai > Signed-off-by: Usama Arif > --- > 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