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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 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 Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: AF86D80006 X-Stat-Signature: dagy51be6kobjz98mujk1pzpfgimofuo X-Rspam-User: X-HE-Tag: 1722352478-748630 X-HE-Meta: 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 abVItr5b ETCwC++jq6kmZixCBTIYEpTAgtnRrmvXf/y5JtGWG8rLKa5xsWyZDexTSGULUyJQ3B38l5baqcEhtbdiVM/s3YRtv9pe0NzvFfE9+ZiD5pYKuv1xDiXF9vQjauzcEXEtOqSpRM0IMTJGfmhG2r0eOJ+yVGq6pk6XiB8V6lQfSPbMsvUhaqYFicR3BpXnyyOKPI/BXCr1PipP0CH33J3QcwJtYDVEshVElFdSACwowbz3BGfppw6N/vCTmIaTDlrceaknOvvR3+bjytnBoRLy1BmjrH4ucPZYquf6F5mTGkwHJuLEANZxm06kFq5WwtC46+5uo1FY9XJCpETC/Um4iv0sU8tobI/kOKNoTjPwbl6jzVE/8WHabjr3RzZJBiVRb4aW5XVqCLkZmw8LEj7FiQU2i5DZBeXKxmvj+ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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