Commit 0c2ec32b authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/rmap: introduce and use hugetlb_try_share_anon_rmap() 

hugetlb rmap handling differs quite a lot from "ordinary" rmap code.  For
example, hugetlb currently only supports entire mappings, and treats any
mapping as mapped using a single "logical PTE".  Let's move it out of the
way so we can overhaul our "ordinary" rmap.  implementation/interface.

So let's introduce and use hugetlb_try_dup_anon_rmap() to make all hugetlb
handling use dedicated hugetlb_* rmap functions.

Add sanity checks that we end up with the right folios in the right
functions.

Note that try_to_unmap_one() does not need care.  Easy to spot because
among all that nasty hugetlb special-casing in that function, we're not
using set_huge_pte_at() on the anon path -- well, and that code assumes
that we would want to swapout.

Link: https://lkml.kernel.org/r/20231220224504.646757-6-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarYin Fengwei <fengwei.yin@intel.com>
Reviewed-by: default avatarRyan Roberts <ryan.roberts@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent ebe2e35e

include/linux/rmap.h

+25 −0
Original line number Diff line number Diff line
@@ -227,6 +227,30 @@ static inline int hugetlb_try_dup_anon_rmap(struct folio *folio, 
	return 0;

}



/* See page_try_share_anon_rmap() */

static inline int hugetlb_try_share_anon_rmap(struct folio *folio)

{

	VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);

	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);

	VM_WARN_ON_FOLIO(!PageAnonExclusive(&folio->page), folio);



	/* Paired with the memory barrier in try_grab_folio(). */

	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))

		smp_mb();



	if (unlikely(folio_maybe_dma_pinned(folio)))

		return -EBUSY;

	ClearPageAnonExclusive(&folio->page);



	/*

	 * This is conceptually a smp_wmb() paired with the smp_rmb() in

	 * gup_must_unshare().

	 */

	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))

		smp_mb__after_atomic();

	return 0;

}



static inline void hugetlb_add_file_rmap(struct folio *folio)

{

	VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
@@ -331,6 +355,7 @@ static inline int page_try_dup_anon_rmap(struct page *page, bool compound, 
 */

static inline int page_try_share_anon_rmap(struct page *page)

{

	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));

	VM_BUG_ON_PAGE(!PageAnon(page) || !PageAnonExclusive(page), page);



	/* device private pages cannot get pinned via GUP. */

mm/rmap.c

+10 −5
Original line number Diff line number Diff line
@@ -2149,12 +2149,17 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, 
				       !anon_exclusive, subpage);



			/* See page_try_share_anon_rmap(): clear PTE first. */

			if (folio_test_hugetlb(folio)) {

				if (anon_exclusive &&

			    page_try_share_anon_rmap(subpage)) {

				if (folio_test_hugetlb(folio))

				    hugetlb_try_share_anon_rmap(folio)) {

					set_huge_pte_at(mm, address, pvmw.pte,

							pteval, hsz);

				else

					ret = false;

					page_vma_mapped_walk_done(&pvmw);

					break;

				}

			} else if (anon_exclusive &&

				   page_try_share_anon_rmap(subpage)) {

				set_pte_at(mm, address, pvmw.pte, pteval);

				ret = false;

				page_vma_mapped_walk_done(&pvmw);