Messages in this thread | | | From | Daniel Mentz <> | Date | Fri, 2 Nov 2018 14:16:35 -0700 | Subject | Re: lib/genalloc |
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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.
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