[Patch v2] mm/huge_memory: add pmd folio to ds_queue in do_huge_zero_wp_pmd()

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

We add pmd folio into ds_queue on the first page fault in
__do_huge_pmd_anonymous_page(), so that we can split it in case of
memory pressure. This should be the same for a pmd folio during wp
page fault.

Commit 1ced09e0331f ("mm: allocate THP on hugezeropage wp-fault") miss
to add it to ds_queue, which means system may not reclaim enough memory
in case of memory pressure even the pmd folio is under used.

Move deferred_split_folio() into map_anon_folio_pmd() to make the pmd
folio installation consistent.

Fixes: 1ced09e0331f ("mm: allocate THP on hugezeropage wp-fault")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Dev Jain <dev.jain@arm.com>
Cc: <stable@vger.kernel.org>

---
v2:
  * add fix, cc stable and put description about the flow of current
    code
  * move deferred_split_folio() into map_anon_folio_pmd()
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1b81680b4225..f13de93637bf 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1232,6 +1232,7 @@ static void map_anon_folio_pmd(struct folio *folio, pmd_t *pmd,
 	count_vm_event(THP_FAULT_ALLOC);
 	count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
 	count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
+	deferred_split_folio(folio, false);
 }
 
 static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
@@ -1272,7 +1273,6 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
 		map_anon_folio_pmd(folio, vmf->pmd, vma, haddr);
 		mm_inc_nr_ptes(vma->vm_mm);
-		deferred_split_folio(folio, false);
 		spin_unlock(vmf->ptl);
 	}
 
-- 
2.34.1