On 12/08/22 19:33, Matthew Wilcox wrote: > On Thu, Dec 08, 2022 at 10:06:07AM -0800, Sidhartha Kumar wrote: > > On 12/7/22 6:27 PM, John Hubbard wrote: > > > On 12/7/22 17:42, Sidhartha Kumar wrote: > > 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. > > None of the above! > > Whatever we're calling this function *it does not belong* in mm.h. > Anything outside the MM calling it is going to be a disaster -- can you > imagine what will happen if a filesystem or device driver is handed a > folio and decides "Oh, I'll just change the size of this folio"? It is > an attractive nuisance and should be confined to mm/internal.h *at best*. I suspect it was placed in mm.h as it is the 'folio version' of set_compound_order which resides in mm.h. But, no need to repeat that unfortunate placement. > > Equally, we *must not have* separate folio_set_order() and > folio_set_nr_pages(). These are the same thing! They must be kept > in sync! If we are to have a folio_set_order() instead of open-coding > it, then it should also update nr_pages. Ok. Agree. > So, given that this is now an internal-to-mm, if not internal-to-hugetlb > function, I see no reason that it should not handle the case of 0. > I haven't studied what hugetlb_dissolve does, or why it can't use the > standard split_folio(), but I'm sure there's a good reason. The hugetlb code is changing the compound page/folio it created from a set of individual pages back to individual pages so they can be returned to the low level allocator. Somewhat like what page_alloc/page_free do. split_folio is overkill. split_page would be a closer match. It makes perfect sense to put the function in mm internal.h. Thanks, -- Mike Kravetz
