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 6TMn5Qsq mYOeOQqE8TVb/fMJGcoc4a78sLsvrWPbQnrnIcZpBIPEiWAVUrIUAGCZ6V3h5TZXioF+w4X2nXhSuDZEEcmoydWD393G8rIAZOgIh64hSAyT9L64= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/7/22 6:27 PM, John Hubbard wrote: > On 12/7/22 17:42, Sidhartha Kumar wrote: >>> Wouldn't it be better to instead just create a new function for that >>> case, such as: >>> >>>      dissolve_large_folio() >>> >> >> Prior to the folio conversion, the helper function >> __destroy_compound_gigantic_page() did: >> >>      set_compound_order(page, 0); >> #ifdef CONFIG_64BIT >>      page[1].compound_nr = 0; >> #endif >> >> as part of dissolving the page. My goal for this patch was to create a >> function that would encapsulate that segment of code with a single >> call of folio_set_compound_order(folio, 0). set_compound_order() does >> not set compound_nr to 0 when 0 is passed in to the order argument so >> explicitly setting it is required. I don't think a separate >> dissolve_large_folio() function for the hugetlb case is needed as >> __destroy_compound_gigantic_folio() is pretty concise as it is. >> > > Instead of "this is abusing function X()" comments, we should prefer > well-named functions that do something understandable. And you can get > that by noticing that folio_set_compound_order() collapses down to > nearly nothing in the special "order 0" case. So just inline that code > directly into __destroy_compound_gigantic_folio(), taking a moment to > fill in and consolidate the CONFIG_64BIT missing parts in mm.h. > > And now you can get rid of this cruft and "abuse" comment, and instead > just end up with two simple lines of code that are crystal clear--as > they should be, in a "__destroy" function. Like this: > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 105878936485..cf227ed00945 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1754,6 +1754,7 @@ static inline void set_page_links(struct page > *page, enum zone_type zone, >  #endif >  } > > +#ifdef CONFIG_64BIT >  /** >   * folio_nr_pages - The number of pages in the folio. >   * @folio: The folio. > @@ -1764,13 +1765,32 @@ static inline long folio_nr_pages(struct folio > *folio) >  { >      if (!folio_test_large(folio)) >          return 1; > -#ifdef CONFIG_64BIT >      return folio->_folio_nr_pages; > +} > + > +static inline void folio_set_nr_pages(struct folio *folio, long nr_pages) > +{ > +    folio->_folio_nr_pages = nr_pages; > +} >  #else > +/** > + * folio_nr_pages - The number of pages in the folio. > + * @folio: The folio. > + * > + * Return: A positive power of two. > + */ > +static inline long folio_nr_pages(struct folio *folio) > +{ > +    if (!folio_test_large(folio)) > +        return 1; >      return 1L << folio->_folio_order; > -#endif >  } > > +static inline void folio_set_nr_pages(struct folio *folio, long nr_pages) > +{ > +} > +#endif > + >  /** >   * folio_next - Move to the next physical folio. >   * @folio: The folio we're currently operating on. > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index e3500c087893..b507a98063e6 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1344,7 +1344,8 @@ static void > __destroy_compound_gigantic_folio(struct folio *folio, >              set_page_refcounted(p); >      } > > -    folio_set_compound_order(folio, 0); > +    folio->_folio_order = 0; > +    folio_set_nr_pages(folio, 0); >      __folio_clear_head(folio); >  } > > > Yes? This works for me, I will take this approach along with Muchun's feedback about a wrapper function so as not to touch _folio_order directly and send out a new version. One question I have is if I should then get rid of folio_set_compound_order() as hugetlb is the only compound page user I've converted to folios so far and its use can be replaced by the suggested folio_set_nr_pages() and folio_set_order(). Hugetlb also has one has one call to folio_set_compound_order() with a non-zero order, should I replace this with a call to folio_set_order() and folio_set_nr_pages() as well, or keep folio_set_compound_order() and remove zero order support and the comment. Please let me know which approach you would prefer. Thanks, Sidhartha Kumar > thanks,