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Wed, 14 Apr 2021 17:07:56 +0000 Subject: Re: [PATCH v7 6/7] mm: Make alloc_contig_range handle in-use hugetlb pages To: Oscar Salvador Cc: Andrew Morton , Vlastimil Babka , David Hildenbrand , Michal Hocko , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210413104747.12177-1-osalvador@suse.de> <20210413104747.12177-7-osalvador@suse.de> <722f9a5e-ef0a-508a-e58a-6c3eacb5d1bd@oracle.com> From: Mike Kravetz Message-ID: <681fac27-9684-48cd-daec-fb82057f2253@oracle.com> Date: Wed, 14 Apr 2021 10:07:54 -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: MWHPR18CA0035.namprd18.prod.outlook.com (2603:10b6:320:31::21) 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 MWHPR18CA0035.namprd18.prod.outlook.com (2603:10b6:320:31::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4042.16 via Frontend Transport; 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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: 1618420076-107114 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 4/13/21 9:52 PM, Oscar Salvador wrote: > On Tue, Apr 13, 2021 at 03:48:53PM -0700, Mike Kravetz wrote: >> The label free_new is: >> >> free_new: >> spin_unlock_irq(&hugetlb_lock); >> __free_pages(new_page, huge_page_order(h)); >> >> return ret; >> >> So, we are locking and immediately unlocking without any code in >> between. Usually, I don't like like multiple labels before return. >> However, perhaps we should add another to avoid this unnecessary >> cycle. On the other hand, this is an uncommon race condition so the >> simple code may be acceptable. > > I guess we could have something like: > > free_new: > spin_unlock_irq(&hugetlb_lock); > free_new_nolock: > __free_pages(new_page, huge_page_order(h)); > > return ret; > > And let the retry go to there without locking. But as you said, the > racecondition is rare enough, so I am not sure if this buys us much. > But I can certainly add it if you feel strong about it. No strong feelings. I am fine with it as is. -- Mike Kravetz