Messages in this thread | | | Subject | Re: lib/genalloc | From | Alexey Skidanov <> | Date | Sat, 3 Nov 2018 00:18:22 +0200 |
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On 11/2/18 11:16 PM, Daniel Mentz wrote: > On Fri, Nov 2, 2018 at 1:55 PM Alexey Skidanov > <alexey.skidanov@intel.com> wrote: >> >> >> >> 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? > > Yeah, I guess you could extend genpool_algo_t to include the > information you need i.e. the offset and then provide a modified > version of gen_pool_first_fit_align() that does take your offset into > account. I wouldn't change gen_pool_first_fit_align(), though, because > existing users might depend on the current behavior. > I think that the "fixed" version of gen_pool_first_fit_align() is less restrictive with respect to chunk base address - it will work correctly with arbitrary aligned chunks.
Thanks, Alexey
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