linux-kernel - [PATCH v2 2/2] mm: set pte writable while pte_soft_dirty() is true in do_swap

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Date: Sat,  8 Jun 2024 09:13:58 +1200
From: Barry Song <21cnbao@...il.com>
To: akpm@...ux-foundation.org,
	david@...hat.com,
	linux-mm@...ck.org
Cc: chrisl@...nel.org,
	kasong@...cent.com,
	linux-kernel@...r.kernel.org,
	minchan@...nel.org,
	ryan.roberts@....com,
	surenb@...gle.com,
	v-songbaohua@...o.com,
	willy@...radead.org
Subject: [PATCH v2 2/2] mm: set pte writable while pte_soft_dirty() is true in do_swap_page()

From: Barry Song <v-songbaohua@...o.com>

This patch leverages the new pte_needs_soft_dirty_wp() helper to optimize
a scenario where softdirty is enabled, but the softdirty flag has already
been set in do_swap_page(). In this situation, we can use pte_mkwrite
instead of applying write-protection since we don't depend on write
faults.

Suggested-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Barry Song <v-songbaohua@...o.com>
---
 mm/memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index db9130488231..a063e489446d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4322,7 +4322,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	if (!folio_test_ksm(folio) &&
 	    (exclusive || folio_ref_count(folio) == 1)) {
 		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
-		    !vma_soft_dirty_enabled(vma)) {
+		    !pte_needs_soft_dirty_wp(vma, pte)) {
 			pte = pte_mkwrite(pte, vma);
 			if (vmf->flags & FAULT_FLAG_WRITE) {
 				pte = pte_mkdirty(pte);
-- 
2.34.1