>On 5/16/20 12:47 AM, Hushijie wrote: >>> On 5/14/20 7:31 AM, Shijie Hu wrote: >>>> + if (mm->get_unmapped_area == arch_get_unmapped_area) >>>> + return hugetlb_get_unmapped_area_bottomup(file, addr, len, >>>> + pgoff, flags); >>>> + return hugetlb_get_unmapped_area_topdown(file, addr, len, >>>> + pgoff, flags); >>> >>> I like this code using the value of mm->get_unmapped_area to determine >>> which routine to call. It is used by a few architectures. However, I >>> noticed that on at least one architecture (powerpc) mm->get_unmapped_area >>> may be assigned to routines other than arch_get_unmapped_area or >>> arch_get_unmapped_area_topdown. In such a case, we would call the 'new' >>> topdown routine. I would prefer that we call the bottomup routine in this >>> default case. >>> >>> In reality, this does not impact powerpc as that architecture has it's >>> own hugetlb_get_unmapped_area routine. >>> >> >> Yes, I also noticed this before, powerpc uses radix__arch_get_unmapped_area*() >> when CONFIG_PPC_RADIX_MMU opened as 'y' and radix_enabled() returns >> true. However, powerpc implemented its own hugetlb_get_unmapped_area(). This >> patch actually has no effect on powerpc. >> >>> Because of this, I suggest we add a comment above this code and switch >>> the if/else order. For example, >>> >>> + /* >>> + * Use mm->get_unmapped_area value as a hint to use topdown routine. >>> + * If architectures have special needs, they should define their own >>> + * version of hugetlb_get_unmapped_area. >>> + */ >>> + if (mm->get_unmapped_area == arch_get_unmapped_area_topdown) >>> + return hugetlb_get_unmapped_area_topdown(file, addr, len, >>> + pgoff, flags); >>> + return hugetlb_get_unmapped_area_bottomup(file, addr, len, >>> + pgoff, flags); >>> >>> Thoughts? >>> -- >>> Mike Kravetz >>> >> I agree with you. It's clever to switch the if/else order. If there is such >> a case, mm->get_unmapped_area() is neihter arch_get_unmapped_area() nor >> arch_get_unmapped_area_topdown(), it is indeed more appropriate to make the >> bottomup routine as the default behavior. >> >> May I put this code and comment you show above into patch v6 and add >> "Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>" to it? > >Feel free to add this code and my Signed-off-by. > >I assume this still works for your use case. Correct? >-- >Mike Kravetz > Yes, It still works for our use case. Thanks for your replies and suggestions, I will submit patch v6 later. -- Shijie Hu
