>> Why does "page allocation failure" occur whereas there are still "58*4096kB >> (C)"(*I think it indicates there are 58 order 10 memory could be used*) >> could be used? >> >> Here is the related log: >> >> [ 2161.623563] xxxx: page allocation failure: order:10, >> mode:0x2084020(GFP_ATOMIC|__GFP_COMP) > >If you look at the source for alloc_ap_req(), you find it wants GFP_ATOMIC, not >CMA. And your box is fresh out of contiguous order-10 spaces that aren't CMA, >and you're down to your last 3 order-9 flagged as (UEC).
Thank you for the clarification. I understand it on a deeper level with your help. Why doesn't the kernel use two memory blocks whose size is 2048KB(i.e.*oder 9 *) instead of one block *order 10 *(you see, there are still three free blocks and 2048KB*2=4096KB equivalent to the memory size of order 10)? >If you look at the source for alloc_ap_req(), you find it wants GFP_ATOMIC, not >CMA. I followed your advice and read the related source code carefully. It's corresponding to the log(i.e. mode:0x2084020(GFP_ATOMIC|__GFP_COMP) ). Thank you for your attention to this matter. Look forward to hearing from you. Best regards. Valdis Klētnieks <valdis.kletni...@vt.edu> 于2020年6月19日周五 下午12:48写道: > On Thu, 18 Jun 2020 14:21:05 +0800, sunshiong said: > > > Why does "page allocation failure" occur whereas there are still > "58*4096kB > > (C)"(*I think it indicates there are 58 order 10 memory could be used*) > > could be used? > > > > Here is the related log: > > > > [ 2161.623563] xxxx: page allocation failure: order:10, > > mode:0x2084020(GFP_ATOMIC|__GFP_COMP) > > Most likely, the allocation wanted some other type of allocation. > The (C) on the order-10 says it's an CMA area. > > static const char types[MIGRATE_TYPES] = { > [MIGRATE_UNMOVABLE] = 'U', > [MIGRATE_MOVABLE] = 'M', > [MIGRATE_RECLAIMABLE] = 'E', > [MIGRATE_HIGHATOMIC] = 'H', > #ifdef CONFIG_CMA > [MIGRATE_CMA] = 'C', > #endif > #ifdef CONFIG_MEMORY_ISOLATION > [MIGRATE_ISOLATE] = 'I', > #endif > > If the call was for an unmovable, movable, reclaimable, or highatomic > allocation, you lose. > > If you look at the source for alloc_ap_req(), you find it wants > GFP_ATOMIC, not > CMA. And your box is fresh out of contiguous order-10 spaces that aren't > CMA, > and you're down to your last 3 order-9 flagged as (UEC). > > I admit I find it a tad suspicious that the USB gadget driver asks for a 4M > chunk of memory. Does USB actually support single transfers that large? > (I'm > not a USB expert) > >
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