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[195.135.220.15]) by mx.google.com with ESMTPS id a9si12423964ejs.42.2019.07.17.03.56.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Jul 2019 03:56:01 -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 75F31B048; Wed, 17 Jul 2019 10:56:00 +0000 (UTC) Subject: Re: [v2 PATCH 1/2] mm: mempolicy: make the behavior consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified To: Yang Shi , mhocko@kernel.org, mgorman@techsingularity.net, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1561162809-59140-1-git-send-email-yang.shi@linux.alibaba.com> <1561162809-59140-2-git-send-email-yang.shi@linux.alibaba.com> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 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 7/16/19 7:18 PM, Yang Shi wrote: >> I think after your patch, you miss putback_movable_pages() in cases >> where some were queued, and later the walk returned -EIO. The previous >> code doesn't miss it, but it's also not obvious due to the multiple if >> (!err) checks. I would rewrite it some thing like this: >> >> if (ret < 0) { >> putback_movable_pages(&pagelist); >> err = ret; >> goto mmap_out; // a new label above up_write() >> } > > Yes, the old code had putback_movable_pages called when !err. But, I > think that is for error handling of mbind_range() if I understand it > correctly since if queue_pages_range() returns -EIO (only MPOL_MF_STRICT > was specified and there was misplaced page) that page list should be > empty . The old code should checked whether that list is empty or not. Hm I guess you're right, returning with EIO means nothing was queued. > So, in the new code I just removed that. > >> >> The rest can have reduced identation now. > > Yes, the goto does eliminate the extra indentation. > >> >>> + else { >>> + err = mbind_range(mm, start, end, new); >>> >>> - if (nr_failed && (flags & MPOL_MF_STRICT)) >>> - err = -EIO; >>> - } else >>> - putback_movable_pages(&pagelist); >>> + if (!err) { >>> + int nr_failed = 0; >>> + >>> + if (!list_empty(&pagelist)) { >>> + WARN_ON_ONCE(flags & MPOL_MF_LAZY); >>> + nr_failed = migrate_pages(&pagelist, new_page, >>> + NULL, start, MIGRATE_SYNC, >>> + MR_MEMPOLICY_MBIND); >>> + if (nr_failed) >>> + putback_movable_pages(&pagelist); >>> + } >>> + >>> + if ((ret > 0) || >>> + (nr_failed && (flags & MPOL_MF_STRICT))) >>> + err = -EIO; >>> + } else >>> + putback_movable_pages(&pagelist); >> While at it, IIRC the kernel style says that when the 'if' part uses >> '{ }' then the 'else' part should as well, and it shouldn't be mixed. > > Really? The old code doesn't have '{ }' for else, and checkpatch doesn't > report any error or warning. Checkpatch probably doesn't catch it, nor did the reviewers of the older code. But coding-style.rst says: Do not unnecessarily use braces where a single statement will do. ... This does not apply if only one branch of a conditional statement is a single statement; in the latter case use braces in both branches: .. code-block:: c if (condition) { do_this(); do_that(); } else { otherwise(); } Thanks, Vlastimil