Path: csiph.com!news.mixmin.net!aioe.org!gothmog.csi.it!bofh.it!news.nic.it!robomod From: Vlastimil Babka Newsgroups: linux.kernel Subject: Re: Suspicious error for CMA stress test Date: Thu, 17 Mar 2016 16:50:02 +0100 Message-ID: References: X-Original-To: Hanjun Guo , Joonsoo Kim User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 39 Organization: linux.* mail to news gateway X-Original-Cc: "Leizhen (ThunderTown)" , Laura Abbott , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Sasha Levin , Laura Abbott , qiuxishi , Catalin Marinas , Will Deacon , Arnd Bergmann , dingtinahong , chenjie6@huawei.com, "linux-mm@kvack.org" X-Original-Date: Thu, 17 Mar 2016 16:43:48 +0100 X-Original-Message-ID: <56EAD0B4.2060807@suse.cz> X-Original-References: <56DD38E7.3050107@huawei.com> <56DDCB86.4030709@redhat.com> <56DE30CB.7020207@huawei.com> <56DF7B28.9060108@huawei.com> <56E2FB5C.1040602@suse.cz> <20160314064925.GA27587@js1304-P5Q-DELUXE> <56E662E8.700@suse.cz> <20160314071803.GA28094@js1304-P5Q-DELUXE> <56E92AFC.9050208@huawei.com> <20160317065426.GA10315@js1304-P5Q-DELUXE> <56EA77BC.2090702@huawei.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1359970 On 03/17/2016 10:24 AM, Hanjun Guo wrote: > On 2016/3/17 14:54, Joonsoo Kim wrote: >> On Wed, Mar 16, 2016 at 05:44:28PM +0800, Hanjun Guo wrote: >>> On 2016/3/14 15:18, Joonsoo Kim wrote: >>>> On Mon, Mar 14, 2016 at 08:06:16AM +0100, Vlastimil Babka wrote: >>>>> On 03/14/2016 07:49 AM, Joonsoo Kim wrote: >>>>>> On Fri, Mar 11, 2016 at 06:07:40PM +0100, Vlastimil Babka wrote: >>>>>>> On 03/11/2016 04:00 PM, Joonsoo Kim wrote: >>>>>>> >>>>>>> How about something like this? Just and idea, probably buggy (off-by-one etc.). >>>>>>> Should keep away cost from >>>>>> relatively fewer >pageblock_order iterations. >>>>>> Hmm... I tested this and found that it's code size is a little bit >>>>>> larger than mine. I'm not sure why this happens exactly but I guess it would be >>>>>> related to compiler optimization. In this case, I'm in favor of my >>>>>> implementation because it looks like well abstraction. It adds one >>>>>> unlikely branch to the merge loop but compiler would optimize it to >>>>>> check it once. >>>>> I would be surprised if compiler optimized that to check it once, as >>>>> order increases with each loop iteration. But maybe it's smart >>>>> enough to do something like I did by hand? Guess I'll check the >>>>> disassembly. >>>> Okay. I used following slightly optimized version and I need to >>>> add 'max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1)' >>>> to yours. Please consider it, too. >>> Hmm, this one is not work, I still can see the bug is there after applying >>> this patch, did I miss something? >> I may find that there is a bug which was introduced by me some time >> ago. Could you test following change in __free_one_page() on top of >> Vlastimil's patch? >> >> -page_idx = pfn & ((1 << max_order) - 1); >> +page_idx = pfn & ((1 << MAX_ORDER) - 1); > > I tested Vlastimil's patch + your change with stress for more than half hour, the bug > I reported is gone :) Oh, ok, will try to send proper patch, once I figure out what to write in the changelog :)