Re: [Patch v2] mm/huge_memory: use end_folio to terminate anonymous folio remapping

[Wei Yang <richard.weiyang@gmail.com>]

On Thu, Dec 18, 2025 at 10:58:36AM +0100, David Hildenbrand (Red Hat) wrote:
>On 12/15/25 10:15, Barry Song wrote:
>> On Mon, Dec 15, 2025 at 4:43 PM Wei Yang <richard.weiyang@gmail.com> wrote:
>> > 
>> > On Mon, Dec 15, 2025 at 10:31:15AM +0800, Barry Song wrote:
>> > > On Mon, Dec 15, 2025 at 8:49 AM Wei Yang <richard.weiyang@gmail.com> wrote:
>> > > > 
>> > > > After splitting a large folio, it is necessary to remap the resulting
>> > > > anonymous folios.
>> > > > 
>> > > > The current implementation determines the end of the remapping process
>> > > > by counting the number of pages that have been processed.
>> > > > 
>> > > > Since the final folio in the sequence, end_folio, is already known and
>> > > > tracked, this commit refactors the remapping loop to leverage end_folio
>> > > > as the termination marker.
>> > > > 
>> > > > Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> > > > Cc: Zi Yan <ziy@nvidia.com>
>> > > > 
>> > > > ---
>> > > > v2: move folio assignment in loop
>> > > > ---
>> > > >   mm/huge_memory.c | 13 ++++---------
>> > > >   1 file changed, 4 insertions(+), 9 deletions(-)
>> > > > 
>> > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> > > > index 40cf59301c21..fe812d9c7807 100644
>> > > > --- a/mm/huge_memory.c
>> > > > +++ b/mm/huge_memory.c
>> > > > @@ -3423,20 +3423,15 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr,
>> > > >          return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio);
>> > > >   }
>> > > > 
>> > > > -static void remap_page(struct folio *folio, unsigned long nr, int flags)
>> > > > +static void remap_page(struct folio *folio, struct folio *end_folio, int flags)
>> > > >   {
>> > > 
>> > > Do we actually see an improvement in readability or performance?
>> > > The existing code feels a bit more readable to me; nr is clearly
>> > > the number of pages :-)
>> > > 
>> > 
>> > Hi, Barry,
>> > 
>> > Thanks for your review.
>> > 
>> > Currently end_folio has been used in __folio_split() and
>> > __folio_freeze_and_split_unmapped() as a termination marker. So continue to
>> > use end_folio here as a termination marker looks consistent and improves
>> > readability to me.
>> 
>> In both cases the variables are temporary, and they look fine within their
>> own self-documented contexts.
>> 
>> Now that we’re crossing two functions in the context of remap_page(), this
>> doesn’t seem to be the case, though.
>> 
>> > 
>> > But yeah, this is my personal preference. If it is not the case, I am fine to
>> > keep as it is now. :-)
>> 
>> I personally find the existing code clearer, but I’m also okay if
>> others like your new approach more.
>
>Me too. Well, the existing code could be cleaned up
>* nr -> nr_pages
>* remove i and subtract from nr_pages instead
>

Sorry for my poor taste :-)

Is this what you expect?

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1db9cfb09533..b8ee33318a60 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3423,17 +3423,15 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr,
 	return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio);
 }
 
-static void remap_page(struct folio *folio, unsigned long nr, int flags)
+static void remap_page(struct folio *folio, unsigned long nr_pages, int flags)
 {
-	int i = 0;
-
 	/* If unmap_folio() uses try_to_migrate() on file, remove this check */
 	if (!folio_test_anon(folio))
 		return;
 	for (;;) {
 		remove_migration_ptes(folio, folio, RMP_LOCKED | flags);
-		i += folio_nr_pages(folio);
-		if (i >= nr)
+		nr_pages -= folio_nr_pages(folio);
+		if (!nr_pages)
 			break;
 		folio = folio_next(folio);
 	}

>probably more ... :)
>

Don't catch this. Sounds you have more idea on further cleanup?

Glad to hear your insight.

>-- 
>Cheers
>
>David

-- 
Wei Yang
Help you, Help me