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Thu, 25 Mar 2021 17:12:07 +0000 Subject: Re: [PATCH 5/8] hugetlb: call update_and_free_page without hugetlb_lock To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Roman Gushchin , Shakeel Butt , Oscar Salvador , David Hildenbrand , Muchun Song , David Rientjes , Miaohe Lin , Peter Zijlstra , Matthew Wilcox , HORIGUCHI NAOYA , "Aneesh Kumar K . V" , Waiman Long , Peter Xu , Mina Almasry , Hillf Danton , Andrew Morton References: <20210325002835.216118-1-mike.kravetz@oracle.com> <20210325002835.216118-6-mike.kravetz@oracle.com> From: Mike Kravetz Message-ID: Date: Thu, 25 Mar 2021 10:12:05 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: CO2PR04CA0092.namprd04.prod.outlook.com (2603:10b6:104:6::18) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.112] (50.38.35.18) by CO2PR04CA0092.namprd04.prod.outlook.com (2603:10b6:104:6::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3977.26 via Frontend Transport; Thu, 25 Mar 2021 17:12:06 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: ddb74fa9-5610-409a-b394-08d8efb11e9d X-MS-TrafficTypeDiagnostic: SJ0PR10MB4733: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:3513; 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identity=mailfrom; envelope-from=""; helo=userp2130.oracle.com; client-ip=156.151.31.86 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616692344-503774 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: On 3/25/21 3:55 AM, Michal Hocko wrote: > On Wed 24-03-21 17:28:32, Mike Kravetz wrote: >> With the introduction of remove_hugetlb_page(), there is no need for >> update_and_free_page to hold the hugetlb lock. Change all callers to >> drop the lock before calling. >> >> With additional code modifications, this will allow loops which decrease >> the huge page pool to drop the hugetlb_lock with each page to reduce >> long hold times. >> >> The ugly unlock/lock cycle in free_pool_huge_page will be removed in >> a subsequent patch which restructures free_pool_huge_page. >> >> Signed-off-by: Mike Kravetz > > Acked-by: Michal Hocko > > One minor thing below > > [...] >> @@ -2563,22 +2572,37 @@ static void try_to_free_low(struct hstate *h, unsigned long count, >> nodemask_t *nodes_allowed) >> { >> int i; >> + struct list_head page_list; >> + struct page *page, *next; >> >> if (hstate_is_gigantic(h)) >> return; >> >> + /* >> + * Collect pages to be freed on a list, and free after dropping lock >> + */ >> + INIT_LIST_HEAD(&page_list); >> for_each_node_mask(i, *nodes_allowed) { >> - struct page *page, *next; >> struct list_head *freel = &h->hugepage_freelists[i]; >> list_for_each_entry_safe(page, next, freel, lru) { >> if (count >= h->nr_huge_pages) >> - return; >> + goto out; >> if (PageHighMem(page)) >> continue; >> remove_hugetlb_page(h, page, false); >> - update_and_free_page(h, page); >> + INIT_LIST_HEAD(&page->lru); > > What is the point of rhis INIT_LIST_HEAD? Page has been removed from the > list by remove_hugetlb_page so it can be added to a new one without any > reinitialization. remove_hugetlb_page just does a list_del. list_del will poison the pointers in page->lru. The following list_add will then complain about list corruption. I could replace the list_del in remove_hugetlb_page with list_del_init. However, not all callers of remove_hugetlb_page will be adding the page to a list. If we just call update_and_free_page, there is no need to reinitialize the list pointers. Might be better to just use list_del_init in remove_hugetlb_page to avoid any questions like this. -- Mike Kravetz > >> + list_add(&page->lru, &page_list); >> } >> } >> + >> +out: >> + spin_unlock(&hugetlb_lock); >> + list_for_each_entry_safe(page, next, &page_list, lru) { >> + list_del(&page->lru); >> + update_and_free_page(h, page); >> + cond_resched(); >> + } >> + spin_lock(&hugetlb_lock); >> } >> #else >> static inline void try_to_free_low(struct hstate *h, unsigned long count, >> -- >> 2.30.2 >> >