linux-kernel - [PATCH v4 3/4] mm/khugepaged: unify collapse pmd clear, flush and free

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Message-Id: <20220126183637.1840960-4-pasha.tatashin@soleen.com>
Date:   Wed, 26 Jan 2022 18:36:36 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, rientjes@...gle.com,
        pjt@...gle.com, weixugc@...gle.com, gthelen@...gle.com,
        mingo@...hat.com, will@...nel.org, rppt@...nel.org,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        aneesh.kumar@...ux.ibm.com, jirislaby@...nel.org,
        songmuchun@...edance.com, qydwhotmail@...il.com, hughd@...gle.com,
        ziy@...dia.com, anshuman.khandual@....com
Subject: [PATCH v4 3/4] mm/khugepaged: unify collapse pmd clear, flush and free

Unify the code that flushes, clears pmd entry, and frees the PTE table
level into a new function collapse_and_free_pmd().

This clean-up is useful as in the next patch we will add another call to
this function to iterate through PTE prior to freeing the level for page
table check.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Acked-by: David Rientjes <rientjes@...gle.com>
---
 mm/khugepaged.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 35f14d0a00a6..30e59e4af272 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1416,6 +1416,19 @@ static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
 	return 0;
 }
 
+static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
+				  unsigned long addr, pmd_t *pmdp)
+{
+	spinlock_t *ptl;
+	pmd_t pmd;
+
+	ptl = pmd_lock(vma->vm_mm, pmdp);
+	pmd = pmdp_collapse_flush(vma, addr, pmdp);
+	spin_unlock(ptl);
+	mm_dec_nr_ptes(mm);
+	pte_free(mm, pmd_pgtable(pmd));
+}
+
 /**
  * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
  * address haddr.
@@ -1433,7 +1446,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
 	struct vm_area_struct *vma = find_vma(mm, haddr);
 	struct page *hpage;
 	pte_t *start_pte, *pte;
-	pmd_t *pmd, _pmd;
+	pmd_t *pmd;
 	spinlock_t *ptl;
 	int count = 0;
 	int i;
@@ -1509,12 +1522,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
 	}
 
 	/* step 4: collapse pmd */
-	ptl = pmd_lock(vma->vm_mm, pmd);
-	_pmd = pmdp_collapse_flush(vma, haddr, pmd);
-	spin_unlock(ptl);
-	mm_dec_nr_ptes(mm);
-	pte_free(mm, pmd_pgtable(_pmd));
-
+	collapse_and_free_pmd(mm, vma, haddr, pmd);
 drop_hpage:
 	unlock_page(hpage);
 	put_page(hpage);
@@ -1552,7 +1560,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 	struct vm_area_struct *vma;
 	struct mm_struct *mm;
 	unsigned long addr;
-	pmd_t *pmd, _pmd;
+	pmd_t *pmd;
 
 	i_mmap_lock_write(mapping);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
@@ -1591,14 +1599,8 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 		 * reverse order. Trylock is a way to avoid deadlock.
 		 */
 		if (mmap_write_trylock(mm)) {
-			if (!khugepaged_test_exit(mm)) {
-				spinlock_t *ptl = pmd_lock(mm, pmd);
-				/* assume page table is clear */
-				_pmd = pmdp_collapse_flush(vma, addr, pmd);
-				spin_unlock(ptl);
-				mm_dec_nr_ptes(mm);
-				pte_free(mm, pmd_pgtable(_pmd));
-			}
+			if (!khugepaged_test_exit(mm))
+				collapse_and_free_pmd(mm, vma, addr, pmd);
 			mmap_write_unlock(mm);
 		} else {
 			/* Try again later */
-- 
2.35.0.rc0.227.g00780c9af4-goog