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[91.12.98.6]) by smtp.gmail.com with ESMTPSA id 3sm6752968wms.30.2021.04.26.01.37.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 26 Apr 2021 01:37:24 -0700 (PDT) To: "lipeifeng@oppo.com" , Vlastimil Babka , peifengl55 , schwidefsky , "heiko.carstens" , zhangshiming , zhouhuacai , guoweichao , guojian Cc: linux-s390 , linux-kernel , linux-mm References: <20210414023803.937-1-lipeifeng@oppo.com> <2021042611194631963076@oppo.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [RFC] mm: support multi_freearea to the reduction of external fragmentation Message-ID: <7dcc87f5-9ae5-613a-0cf4-820334592b90@redhat.com> Date: Mon, 26 Apr 2021 10:37:11 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <2021042611194631963076@oppo.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26.04.21 05:19, lipeifeng@oppo.com wrote: > > >> Let's consider part 3 only and ignore the 1) multi freearea (which might > >> be problematic with sparcity) and 2) the modified allocation scheme > >> (which doesn't yet quite sense to me yet, e.g., because we group by > >> mobility and have compaction in place; I assume this really only helps > >> in some special cases -- like the test case you are giving; I might be > >> wrong) > >> Right now, we decide whether to but to head or tail based on how likely > >> it is that we might merge to a higher-order page (buddy_merge_likely()) > >> in the future. So we only consider the current "neighborhood" of the > >> page we're freeing. As we restrict our neighborhood to MAX_ORDER - 1 > >> pages (what we can actually merge). Of course, we can easily be wrong > >> here. Grouping by movability and compaction only helps to some degree I > >> guess. > >> AFAIK, what you propose is basing the decisions where to place a page > >> (in addition?) on a median_pfn. Without 1) and 2) I cannot completely > >> understand if 3) itself would help at all (and how to set the > >> median_pfn). But it would certainly be interesting if we can tweak the > >> current logic to better identify merge targets simply by tweaking > >> buddy_merge_likely() or the assumptions it is making. > > > > Hi David Hildenbrand，Vlastimil Babka: >     Thank you very much indeed for advices. > >>> 2) the modified allocation scheme > >> (which doesn't yet quite sense to me yet, e.g., because we group by > >> mobility and have compaction in place; I assume this really only helps > >> in some special cases -- like the test case you are giving; >  --------------------------------------------------------------------------------- > 1) Divide memory into several segments by pages-PFN > 2) Select the corresponding freearea to alloc-pages >     These two parts art for the same purpose: > low-order-pages allocation will be concentrated in the front area of > physical memory > so that few memory-pollution in the back area of memory, the sussessful > probablity > of high-order allocation would be improved. > >     I think that it would help in almost all cases of high-oder-pages > allocation, instead >     of special case, because it can let more high-order free-pages in > buddy, example: See, and I am not convinced that this is the case, because you really only report one example (Monkey) and I have to assume it is a special case then. > > * when user alloc 64K bytes, if the unit is page(4K bytes) and it > needs to 16 times. > > if the unit is 64Kbytes, it only takes once. > > * if there are more free-high-order-pages in buddy that few > compact-stall in > > alloction-process, the allocstall-time would be shortened. > >     We tested the speed of the high-orders-pages(order=4 and order = 8) > allocation > after monkey and found that it increased by more than 18%. > And you don't mention what the baseline configuration was. For example, how was compaction configured? Just to clarify, what is monkey? Monkey HTTP server? MonkeyTest disk benchmark? UI/Application Exerciser Monkey? > 3) Adjust the location of free-pages in the free_list >>>Without 1) and 2) I cannot completely > >>understand if 3) itself would help at all (and how to set the median_pfn) > ----------------------------------------------------------------------------------------------------- >     Median_pfn is set by the range of pages-PFN of free_area. if part > 3) would be tried separately >     without 1) and 2), the simple setting is the median of the entire > memory. But i think it will play the > better role in optimization based on the 1) and 2). > > > > >> Last but not least, there have to be more benchmarks and test cases that > >> proof that other workload won't be degraded to a degree that people > >> care; as one example, this includes runtime overhead when >>> allocating/freeing pages. > --------------------------------------------- > 1. For modification of buddy: the modified allocation scheme 1)+2) >     Is thers any standard detailed test-list  of the modified > allocation in the community? like benchmarks > or any other tests? if  i pass the test required by communiry that can > proof the patch will not degraded > to a degree that people care and can merge it in the baseline? IIRC, there are plenty. One example is will-it-scale. Have a look at https://github.com/intel/lkp-tests.git -- Thanks, David / dhildenb