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,