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
