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[79.242.52.184]) by smtp.gmail.com with ESMTPSA id d2sm7152790wra.61.2021.12.17.04.27.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Dec 2021 04:27:10 -0800 (PST) Message-ID: <88ce4f53-587b-c18a-9694-a3e173e6e030@redhat.com> Date: Fri, 17 Dec 2021 13:27:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH 1/2] mm: cma: fix allocation may fail sometimes Content-Language: en-US To: Aisheng Dong , "linux-mm@kvack.org" Cc: "linux-kernel@vger.kernel.org" , "dongas86@gmail.com" , "linux-arm-kernel@lists.infradead.org" , Jason Liu , Leo Li , Abel Vesa , "shawnguo@kernel.org" , dl-linux-imx , "akpm@linux-foundation.org" , "m.szyprowski@samsung.com" , "lecopzer.chen@mediatek.com" , "vbabka@suse.cz" , "stable@vger.kernel.org" , Shijie Qin References: <20211215080242.3034856-1-aisheng.dong@nxp.com> <20211215080242.3034856-2-aisheng.dong@nxp.com> <783f64f5-3a55-6c42-a740-19a12c2c7321@redhat.com> <7d9b7e5f-a6c0-2079-90e7-c02aaeb1f4c0@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 17.12.21 04:44, Aisheng Dong wrote: >> From: David Hildenbrand >> Sent: Thursday, December 16, 2021 6:57 PM >> >> On 16.12.21 03:54, Aisheng Dong wrote: >>>> From: David Hildenbrand >>>> Sent: Wednesday, December 15, 2021 8:31 PM >>>> >>>> On 15.12.21 09:02, Dong Aisheng wrote: >>>>> We met dma_alloc_coherent() fail sometimes when doing 8 VPU decoder >>>>> test in parallel on a MX6Q SDB board. >>>>> >>>>> Error log: >>>>> cma: cma_alloc: linux,cma: alloc failed, req-size: 148 pages, ret: >>>>> -16 >>>>> cma: number of available pages: >>>>> >>>> >> 3@125+20@172+12@236+4@380+32@736+17@2287+23@2473+20@3607 >>>> 6+99@40477+108 >>>>> @40852+44@41108+20@41196+108@41364+108@41620+ >>>>> >>>> >> 108@42900+108@43156+483@44061+1763@45341+1440@47712+20@49 >>>> 324+20@49388+ >>>>> 5076@49452+2304@55040+35@58141+20@58220+20@58284+ >>>>> 7188@58348+84@66220+7276@66452+227@74525+6371@75549=> >>>> 33161 free of >>>>> 81920 total pages >>>>> >>>>> When issue happened, we saw there were still 33161 pages (129M) free >>>>> CMA memory and a lot available free slots for 148 pages in CMA >>>>> bitmap that we want to allocate. >>>>> >>>>> If dumping memory info, we found that there was also ~342M normal >>>>> memory, but only 1352K CMA memory left in buddy system while a lot >>>>> of pageblocks were isolated. >>>>> >>>>> Memory info log: >>>>> Normal free:351096kB min:30000kB low:37500kB high:45000kB >>>> reserved_highatomic:0KB >>>>> active_anon:98060kB inactive_anon:98948kB active_file:60864kB >>>> inactive_file:31776kB >>>>> unevictable:0kB writepending:0kB present:1048576kB >>>> managed:1018328kB mlocked:0kB >>>>> bounce:0kB free_pcp:220kB local_pcp:192kB free_cma:1352kB >>>>> lowmem_reserve[]: 0 0 0 >>>>> Normal: 78*4kB (UECI) 1772*8kB (UMECI) 1335*16kB (UMECI) 360*32kB >>>> (UMECI) 65*64kB (UMCI) >>>>> 36*128kB (UMECI) 16*256kB (UMCI) 6*512kB (EI) 8*1024kB (UEI) >>>> 4*2048kB (MI) 8*4096kB (EI) >>>>> 8*8192kB (UI) 3*16384kB (EI) 8*32768kB (M) = 489288kB >>>>> >>>>> The root cause of this issue is that since commit a4efc174b382 >>>>> ("mm/cma.c: remove redundant cma_mutex lock"), CMA supports >>>> concurrent >>>>> memory allocation. It's possible that the pageblock process A try to >>>>> alloc has already been isolated by the allocation of process B >>>>> during memory migration. >>>>> >>>>> When there're multi process allocating CMA memory in parallel, it's >>>>> likely that other the remain pageblocks may have also been isolated, >>>>> then CMA alloc fail finally during the first round of scanning of >>>>> the whole available CMA bitmap. >>>> >>>> I already raised in different context that we should most probably >>>> convert that -EBUSY to -EAGAIN -- to differentiate an actual >>>> migration problem from a simple "concurrent allocations that target the >> same MAX_ORDER -1 range". >>>> >>> >>> Thanks for the info. Is there a patch under review? >> >> No, and I was too busy for now to send it out. >> >>> BTW i wonder that probably makes no much difference for my patch since >>> we may prefer retry the next pageblock rather than busy waiting on the >> same isolated pageblock. >> >> Makes sense. BUT as of now we isolate not only a pageblock but a >> MAX_ORDER -1 page (e.g., 2 pageblocks on x86-64 (!) ). So you'll have the >> same issue in that case. > > Yes, should I change to try next MAX_ORDER_NR_PAGES or keep as it is > and let the core to improve it later? > > I saw there's a patchset under review which is going to remove the > MAX_ORDER - 1 alignment requirement for CMA. > https://patchwork.kernel.org/project/linux-mm/cover/20211209230414.2766515-1-zi.yan@sent.com/ > > Once it's merged, I guess we can back to align with pageblock rather > than MAX_ORDER-1. While the goal is to get rid of the alignment requirement, we might still have to isolate all applicable MAX_ORDER-1 pageblocks. Depends on what we can or cannot achieve easily :) -- Thanks, David / dhildenb