Re: [PATCH 1/2] mm: cma: fix allocation may fail sometimes
From: David Hildenbrand <hidden>
Date: 2021-12-15 12:30:59
Also in:
linux-mm, lkml, stable
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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel