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[195.135.220.15]) by mx.google.com with ESMTPS id n14si82030edd.269.2019.03.29.01.54.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 Mar 2019 01:54:42 -0700 (PDT) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3B998AE3F; Fri, 29 Mar 2019 08:54:42 +0000 (UTC) Subject: Re: [PATCH] mm/compaction: fix missed direct_compaction setting for non-direct compaction To: Yafang Shao Cc: Michal Hocko , mgorman@techsingularity.net, Andrew Morton , Linux MM , shaoyafang@didiglobal.com References: <1553848599-6124-1-git-send-email-laoar.shao@gmail.com> <60f6a5fd-e4d3-b615-6f41-cc7dd16d183c@suse.cz> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 3/29/19 9:48 AM, Yafang Shao wrote: > On Fri, Mar 29, 2019 at 4:45 PM Vlastimil Babka wrote: >> >> On 3/29/19 9:36 AM, Yafang Shao wrote: >>> direct_compaction is not initialized for kcompactd or manually triggered >>> compaction (via /proc or /sys). >> >> It doesn't need to, this style of initialization does guarantee that any >> field not explicitly mentioned is initialized to 0/NULL/false... and >> this pattern is used all over the kernel. >> > > Hmm. > You mean the gcc will set the local variable to 0 ? Not local variable, but fields omitted in this "designated initializers" scenario. > Are there any reference to this behavior ? https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html "Omitted fields are implicitly initialized the same as for objects that have static storage duration. " and static objects are implicitly 0