| Message ID | 20211215080242.3034856-2-aisheng.dong@nxp.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: fix cma allocation fail sometimes | expand |
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".
> From: David Hildenbrand <david@redhat.com> > 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? 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. Otherwise, we may meet the same issue as the patch 2/2 wants to address. How do you think? Regards Aisheng > > -- > Thanks, > > David / dhildenb
On 16.12.21 03:54, Aisheng Dong wrote: >> From: David Hildenbrand <david@redhat.com> >> 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.
> From: David Hildenbrand <david@redhat.com> > Sent: Thursday, December 16, 2021 6:57 PM > > On 16.12.21 03:54, Aisheng Dong wrote: > >> From: David Hildenbrand <david@redhat.com> > >> 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. Regards Aisheng > > -- > Thanks, > > David / dhildenb
On 17.12.21 04:44, Aisheng Dong wrote: >> From: David Hildenbrand <david@redhat.com> >> Sent: Thursday, December 16, 2021 6:57 PM >> >> On 16.12.21 03:54, Aisheng Dong wrote: >>>> From: David Hildenbrand <david@redhat.com> >>>> 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 :)
On Fri, Dec 17, 2021 at 8:27 PM David Hildenbrand <david@redhat.com> wrote: > > On 17.12.21 04:44, Aisheng Dong wrote: > >> From: David Hildenbrand <david@redhat.com> > >> Sent: Thursday, December 16, 2021 6:57 PM > >> > >> On 16.12.21 03:54, Aisheng Dong wrote: > >>>> From: David Hildenbrand <david@redhat.com> > >>>> 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 :) > Ok, got it. As that's another story and does not affect us to fix the current kernel problem first that CMA alloc may fail occasionally, I'm going to change to align with MAX_ORDER_NR_PAGES for retries as you pointed out in the next version. Do you have more suggestions for this patchset? Regards Aisheng > > -- > Thanks, > > David / dhildenb >
diff --git a/mm/cma.c b/mm/cma.c index bc9ca8f3c487..1c13a729d274 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -433,6 +433,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned long i; struct page *page = NULL; int ret = -ENOMEM; + int loop = 0; if (!cma || !cma->count || !cma->bitmap) goto out; @@ -460,6 +461,16 @@ struct page *cma_alloc(struct cma *cma, unsigned long count, offset); if (bitmap_no >= bitmap_maxno) { spin_unlock_irq(&cma->lock); + pr_debug("%s(): alloc fail, retry loop %d\n", __func__, loop++); + /* + * rescan as others may finish the memory migration + * and quit if no available CMA memory found finally + */ + if (start) { + schedule(); + start = 0; + continue; + } break; } bitmap_set(cma->bitmap, bitmap_no, bitmap_count);
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. This patch introduces a retry mechanism to rescan CMA bitmap for -EBUSY error in case the target pageblock may has been temporarily isolated by others and released later. Theoretically, this issue can be easily reproduced on ARMv7 platforms with big MAX_ORDER/pageblock e.g. 1G RAM(320M reserved CMA) and 32M pageblock ARM platform: Page block order: 13 Pages per block: 8192 Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Cc: Lecopzer Chen <lecopzer.chen@mediatek.com> Cc: David Hildenbrand <david@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> CC: stable@vger.kernel.org # 5.11+ Fixes: a4efc174b382 ("mm/cma.c: remove redundant cma_mutex lock") Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com> --- mm/cma.c | 11 +++++++++++ 1 file changed, 11 insertions(+)