Messages in this thread | | | From | Daniel Mentz <> | Date | Fri, 2 Nov 2018 12:17:11 -0700 | Subject | Re: lib/genalloc |
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On Thu, Nov 1, 2018 at 10:07 AM Alexey Skidanov <alexey.skidanov@intel.com> wrote: > On 11/1/18 18:48, Stephen Bates wrote: > >> I use gen_pool_first_fit_align() as pool allocation algorithm allocating > >> buffers with requested alignment. But if a chunk base address is not > >> aligned to the requested alignment(from some reason), the returned > >> address is not aligned too. > > > > Alexey > > > > Can you try using gen_pool_first_fit_order_align()? Will that give you the alignment you need? > > > > Stephen > > > > > I think it will not help me. Let's assume that the chunk base address is > 0x2F400000 and I want to allocate 16MB aligned buffer. I get back the > 0x2F400000. I think it happens because of this string in the > gen_pool_alloc_algo(): > > addr = chunk->start_addr + ((unsigned long)start_bit << order); > > and the gen_pool_first_fit_align() implementation that doesn't take into > account the "incorrect" chunk base alignment.
gen_pool_first_fit_align() has no information about the chunk base alignment. Hence, it can't take it into account.
How do you request the alignment in your code?
I agree with your analysis that gen_pool_first_fit_align() performs alignment only with respect to the start of the chunk not the memory address that gen_pool_alloc_algo() returns. I guess a solution would be to only add chunks that satisfy all your alignment requirements. In your case, you must only add chunks that are 16MB aligned. I am unsure whether this is by design, but I believe it's the way that the code currently works.
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