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Thu, 17 Mar 2022 10:12:27 -0700 (PDT) Date: Thu, 17 Mar 2022 10:12:25 -0700 From: Minchan Kim To: Dong Aisheng Cc: David Hildenbrand , Dong Aisheng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, 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 Subject: Re: [PATCH v3 1/2] mm: cma: fix allocation may fail sometimes Message-ID: References: <20220315144521.3810298-1-aisheng.dong@nxp.com> <20220315144521.3810298-2-aisheng.dong@nxp.com> <93480fb1-6992-b992-4c93-0046f3b92d7a@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220317_101230_517596_CD8D2AF6 X-CRM114-Status: GOOD ( 38.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Mar 17, 2022 at 10:26:42PM +0800, Dong Aisheng wrote: > On Thu, Mar 17, 2022 at 6:55 PM David Hildenbrand wrote: > > > > On 15.03.22 15:45, Dong Aisheng wrote: > > > When there're multiple process allocing dma memory in parallel > > > > s/allocing/allocating/ > > > > > by calling dma_alloc_coherent(), it may fail sometimes as follows: > > > > > > 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. Yes, I also have met the problem especially when the multiple threads compete cma allocation. Thanks for bringing up the issue. > > > > > > 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. > > > > s/If/When/ > > > > Will fix them all, thanks. > > > > > > > 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 memory range process A trying > > > to alloc has already been isolated by the allocation of process B during > > > memory migration. > > > > > > The problem here is that the memory range isolated during one allocation > > > by start_isolate_page_range() could be much bigger than the real size we > > > want to alloc due to the range is aligned to MAX_ORDER_NR_PAGES. > > > > > > Taking an ARMv7 platform with 1G memory as an example, when MAX_ORDER_NR_PAGES > > > is big (e.g. 32M with max_order 14) and CMA memory is relatively small > > > (e.g. 128M), there're only 4 MAX_ORDER slot, then it's very easy that > > > all CMA memory may have already been isolated by other processes when > > > one trying to allocate memory using dma_alloc_coherent(). > > > Since current CMA code will only scan one time of whole available CMA > > > memory, then dma_alloc_coherent() may easy fail due to contention with > > > other processes. > > > > > > This patch introduces a retry mechanism to rescan CMA bitmap for -EBUSY > > > error in case the target memory range may has been temporarily isolated > > > by others and released later. > > > > But you patch doesn't check for -EBUSY and instead might retry forever, > > on any allocation error, no? > > > > My patch seems not need check it because there's no chance to retry the loop > in case an non -EBUS error happened earlier. > > for (;;) { > if (bitmap_no >= bitmap_maxno) { > retry_the_whole_loop; > } > > pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit); > ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA, > GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0)); > > if (ret != -EBUSY) > break; > } > > > I'd really suggest letting alloc_contig_range() return -EAGAIN in case > > the isolation failed and handling -EAGAIN only in a special way instead. > > > > Yes, i guess that's another improvement and is applicable. > > > In addition, we might want to stop once we looped to often I assume. > > > > I wonder if really retried un-reasonably too often, we probably may > need figure out > what's going on inside alloc_contig_range() and fix it rather than > return EBUSY error to > users in case there're still a lot of avaiable memories. > So currently i didn't add a maximum retry loop outside. > > Additionaly, for a small CMA system (128M with 32M max_order pages), > the retry would > be frequently when multiple process allocating memory, it also depends > on system running > state, so it's hard to define a reasonable and stable maxinum retry count. IMO, when the CMA see the -EAGAIN, it should put the task into cma->wait_queue and then be woken up by other thread which finish work of the cma. So it's similar with cma_mutex but we don't need to synchronize for !EAGAIN cases and make the cma allocatoin fair. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel