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.kletnieks@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)