On Fri, 19 Jun 2020 14:56:20 +0800, å?ä¸?é¾? sunshilong said: > 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)? Most parts of the kernel, when asking for very high-order allocations, *will* have a fallback strategy to use smaller chunks. So, for instance, if a device need a 1M buffer and supports scatter-gather operations, if 1M of contiguous memory isn't available, the kernel can ask for 4 256K chunks and have the I/O directed into the 4 areas. However, if the memory *has* to be contiguous (for example, no scatter/gather available, or it's for an array data structure), then it can't do that. And in fact, that fallback could very well have happened in this case - I didn't bother chasing back to see if the gadget driver does recovery by allocating multiple smaller chunks. (That's a good "exercise for the student"... :)
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