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From: "Thomas Hellström (VMware)" <thomas_os@shipmail.org>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Thomas Hellstrom <thellstrom@vmware.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Steven Price <steven.price@arm.com>
Subject: [PATCH] mm/mapping_dirty_helpers: Update huge page-table entry callbacks
Date: Mon,  3 Feb 2020 16:43:05 +0100
Message-ID: <20200203154305.15045-1-thomas_os@shipmail.org> (raw)

From: Thomas Hellstrom <thellstrom@vmware.com>

Following the update of pagewalk code
commit a07984d48146 ("mm: pagewalk: add p4d_entry() and pgd_entry()")
we can modify the mapping_dirty_helpers' huge page-table entry callbacks
to avoid splitting when a huge pud or -pmd is encountered.

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Steven Price <steven.price@arm.com>
---
v2: Added R-B from Steven.
---
 mm/mapping_dirty_helpers.c | 42 ++++++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c
index 71070dda9643..2c7d03675903 100644
--- a/mm/mapping_dirty_helpers.c
+++ b/mm/mapping_dirty_helpers.c
@@ -111,26 +111,60 @@ static int clean_record_pte(pte_t *pte, unsigned long addr,
 	return 0;
 }
 
-/* wp_clean_pmd_entry - The pagewalk pmd callback. */
+/*
+ * wp_clean_pmd_entry - The pagewalk pmd callback.
+ *
+ * Dirty-tracking should take place on the PTE level, so
+ * WARN() if encountering a dirty huge pmd.
+ * Furthermore, never split huge pmds, since that currently
+ * causes dirty info loss. The pagefault handler should do
+ * that if needed.
+ */
 static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 			      struct mm_walk *walk)
 {
-	/* Dirty-tracking should be handled on the pte level */
 	pmd_t pmdval = pmd_read_atomic(pmd);
 
+	if (!pmd_trans_unstable(&pmdval))
+		return 0;
+
+	if (pmd_none(pmdval)) {
+		walk->action = ACTION_AGAIN;
+		return 0;
+	}
+
+	/* Huge pmd, present or migrated */
+	walk->action = ACTION_CONTINUE;
 	if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
 		WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
 
 	return 0;
 }
 
-/* wp_clean_pud_entry - The pagewalk pud callback. */
+/*
+ * wp_clean_pud_entry - The pagewalk pud callback.
+ *
+ * Dirty-tracking should take place on the PTE level, so
+ * WARN() if encountering a dirty huge puds.
+ * Furthermore, never split huge puds, since that currently
+ * causes dirty info loss. The pagefault handler should do
+ * that if needed.
+ */
 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
 			      struct mm_walk *walk)
 {
-	/* Dirty-tracking should be handled on the pte level */
 	pud_t pudval = READ_ONCE(*pud);
 
+	if (!pud_trans_unstable(&pudval))
+		return 0;
+
+	if (pud_none(pudval)) {
+		walk->action = ACTION_AGAIN;
+		return 0;
+	}
+
+	/* Huge pud */
+	walk->action = ACTION_CONTINUE;
 	if (pud_trans_huge(pudval) || pud_devmap(pudval))
 		WARN_ON(pud_write(pudval) || pud_dirty(pudval));
 
-- 
2.21.1


             reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-03 15:43 Thomas Hellström (VMware) [this message]
  -- strict thread matches above, loose matches on Subject: below --
2020-01-31 10:00 Thomas Hellström (VMware)
2020-01-31 11:33 ` Steven Price
2020-01-31 14:55   ` Thomas Hellström (VMware)

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