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[91.12.96.155]) by smtp.gmail.com with ESMTPSA id j35sm822030wms.13.2021.12.15.04.30.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Dec 2021 04:30:53 -0800 (PST) Message-ID: <783f64f5-3a55-6c42-a740-19a12c2c7321@redhat.com> Date: Wed, 15 Dec 2021 13:30:52 +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: Dong Aisheng , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, dongas86@gmail.com, linux-arm-kernel@lists.infradead.org, jason.hui.liu@nxp.com, leoyang.li@nxp.com, abel.vesa@nxp.com, shawnguo@kernel.org, linux-imx@nxp.com, akpm@linux-foundation.org, m.szyprowski@samsung.com, lecopzer.chen@mediatek.com, vbabka@suse.cz, stable@vger.kernel.org, shijie.qin@nxp.com References: <20211215080242.3034856-1-aisheng.dong@nxp.com> <20211215080242.3034856-2-aisheng.dong@nxp.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20211215080242.3034856-2-aisheng.dong@nxp.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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@36076+99@40477+108@40852+44@41108+20@41196+108@41364+108@41620+ > 108@42900+108@43156+483@44061+1763@45341+1440@47712+20@49324+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, David / dhildenb