| Message ID | 20220329160440.193848-10-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: COW fixes part 2: reliable GUP pins of anonymous pages | expand |
On 3/29/22 18:04, David Hildenbrand wrote: > We want to mark anonymous pages exclusive, and when using > page_move_anon_rmap() we know that we are the exclusive user, as > properly documented. This is a preparation for marking anonymous pages > exclusive in page_move_anon_rmap(). > > In both instances, we're holding page lock and are sure that we're the > exclusive owner (page_count() == 1). hugetlb already properly uses > page_move_anon_rmap() in the write fault handler. Yeah, note that do_wp_page() used to call page_move_anon_rmap() always since the latter was introduced, until commit 09854ba94c6a ("mm: do_wp_page() simplification"). Probably not intended. > Note that in case of a PTE-mapped THP, we'll only end up calling this > function if the whole THP is only referenced by the single PTE mapping > a single subpage (page_count() == 1); consequently, it's fine to modify > the compound page mapping inside page_move_anon_rmap(). > > Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/huge_memory.c | 2 ++ > mm/memory.c | 1 + > 2 files changed, 3 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index c4526343565a..dd16819c5edc 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1317,6 +1317,8 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf) > try_to_free_swap(page); > if (page_count(page) == 1) { > pmd_t entry; > + > + page_move_anon_rmap(page, vma); > entry = pmd_mkyoung(orig_pmd); > entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); > if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry, 1)) > diff --git a/mm/memory.c b/mm/memory.c > index 03e29c9614e0..4303c0fdcf17 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3303,6 +3303,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) > * and the page is locked, it's dark out, and we're wearing > * sunglasses. Hit it. > */ > + page_move_anon_rmap(page, vma); > unlock_page(page); > wp_page_reuse(vmf); > return VM_FAULT_WRITE;
On 12.04.22 11:26, Vlastimil Babka wrote: > On 3/29/22 18:04, David Hildenbrand wrote: >> We want to mark anonymous pages exclusive, and when using >> page_move_anon_rmap() we know that we are the exclusive user, as >> properly documented. This is a preparation for marking anonymous pages >> exclusive in page_move_anon_rmap(). >> >> In both instances, we're holding page lock and are sure that we're the >> exclusive owner (page_count() == 1). hugetlb already properly uses >> page_move_anon_rmap() in the write fault handler. > > Yeah, note that do_wp_page() used to call page_move_anon_rmap() always since > the latter was introduced, until commit 09854ba94c6a ("mm: do_wp_page() > simplification"). Probably not intended. Yeah, it was buried underneath all that reuse_swap_page() complexity.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index c4526343565a..dd16819c5edc 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1317,6 +1317,8 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf) try_to_free_swap(page); if (page_count(page) == 1) { pmd_t entry; + + page_move_anon_rmap(page, vma); entry = pmd_mkyoung(orig_pmd); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry, 1)) diff --git a/mm/memory.c b/mm/memory.c index 03e29c9614e0..4303c0fdcf17 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3303,6 +3303,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) * and the page is locked, it's dark out, and we're wearing * sunglasses. Hit it. */ + page_move_anon_rmap(page, vma); unlock_page(page); wp_page_reuse(vmf); return VM_FAULT_WRITE;
We want to mark anonymous pages exclusive, and when using page_move_anon_rmap() we know that we are the exclusive user, as properly documented. This is a preparation for marking anonymous pages exclusive in page_move_anon_rmap(). In both instances, we're holding page lock and are sure that we're the exclusive owner (page_count() == 1). hugetlb already properly uses page_move_anon_rmap() in the write fault handler. Note that in case of a PTE-mapped THP, we'll only end up calling this function if the whole THP is only referenced by the single PTE mapping a single subpage (page_count() == 1); consequently, it's fine to modify the compound page mapping inside page_move_anon_rmap(). Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/huge_memory.c | 2 ++ mm/memory.c | 1 + 2 files changed, 3 insertions(+)