Messages in this thread | | | Date | Thu, 8 Dec 2022 14:39:45 -0800 | Subject | Re: [PATCH mm-unstable] mm: clarify folio_set_compound_order() zero support | From | John Hubbard <> |
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On 12/8/22 14:33, Sidhartha Kumar wrote: > On 12/8/22 2:14 PM, John Hubbard wrote: >> On 12/8/22 14:12, Sidhartha Kumar wrote: >>> On 12/8/22 2:01 PM, John Hubbard wrote: >>>> On 12/8/22 13:58, Sidhartha Kumar wrote: >>>>> Thanks John, Mike, Matthew, and Muchun for the feedback. >>>>> >>>>> To summarize this discussion and outline the next version of this patch, the changes I'll make include: >>>>> >>>>> 1) change the name of folio_set_compound_order() to folio_set_order() >>>>> 2) change the placement of this function from mm.h to mm/internal.h >>>>> 3) folio_set_order() will set both _folio_order and _folio_nr_pages and handle the zero order case correctly. >>>>> 4) remove the comment about hugetlb's specific use for zero orders >>>>> 5) improve the style of folio_set_order() by removing ifdefs from inside the function to doing >>>>> >>>>> #ifdef CONFIG_64BIT >>>>> static inline void folio_set_order(struct folio *folio, >>>>> unsigned int order) >>>>> { >>>>> VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); >>>> >>>> Sounds good, except for this part: why is a function named >>>> folio_set_order() BUG-ing on a non-large folio? The naming >>>> is still wrong, perhaps? >>>> >>> >>> This is because the _folio_nr_pages and _folio_order fields are part of the first tail page in the folio. folio_test_large returns if the folio is larger than one page which would be required for setting the fields. >> >> OK, but then as I said, the name is wrong. One can either: >> >> a) handle the non-large case, or >> >> b) rename the function to indicate that it only works on large folios. >> > > Discussed here[1], the BUG_ON line seemed more appropriate over > > if (!folio_test_large(folio)) > return; > > as the misuse would not be silent. I think I would be against renaming the function as I don't see any large folio specific function names for other accessors of tail page fields. Would both the BUG_ON and return on non-large folio be included then?
Actually, if you want the "misuse to not be silent", today's guidelines would point more toward WARN and return, instead of BUG, btw.
I don't think that a survey of existing names is really the final word on what to name this. Names should be accurate, even if other names are less so. How about something like:
large_folio_set_order()
?
> > > [1]: https://lore.kernel.org/linux-mm/20221129225039.82257-1-sidhartha.kumar@oracle.com/T/#m98cf80bb21ae533b7385f2e363c602e2c9e2802d >> >> thanks, > >
thanks, -- John Hubbard NVIDIA
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