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 [thread overview]
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
next reply other threads:[~2020-02-03 15:43 UTC|newest]
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 [PATCH] mm/mapping_dirty_helpers: Update huge page-table entry callbacks Thomas Hellström (VMware)
2020-01-31 11:33 ` Steven Price
2020-01-31 14:55 ` Thomas Hellström (VMware)
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