Messages in this thread | | | Subject | Re: lib/genalloc | From | Alexey Skidanov <> | Date | Fri, 2 Nov 2018 22:56:34 +0200 |
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On 11/2/18 9:17 PM, Daniel Mentz wrote: > 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. >
Daniel,
I think the better solution is to use bitmap_find_next_zero_area_off() that receives the bit offset (CMA allocator uses it to solve the same issue). Of course, we need to pass the chunk base address to the gen_pool_first_fit_align().
What do you think?
Thanks, Alexey
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