[PATCH v1 9/9] s390/vmemmap: avoid memset(PAGE_UNUSED) when adding consecutive sections

David Hildenbrand
2020-07-03T13:39:53Z

Let's avoid memset(PAGE_UNUSED) when adding consecutive sections,
whereby the vmemmap of a single section does not span full PMDs.

Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/s390/mm/vmem.c | 45 ++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 42 insertions(+), 3 deletions(-)

diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index a981ff5d47223..9db15fc864fc8 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -74,7 +74,22 @@ static void vmem_pte_free(unsigned long *table)

#define PAGE_UNUSED 0xFD

-static void vmemmap_use_sub_pmd(unsigned long start, unsigned long end)
+/*
+ * The unused vmemmap range, which was not yet memset(PAGE_UNUSED) ranges
+ * from unused_pmd_start to next PMD_SIZE boundary.
+ */
+unsigned long unused_pmd_start;
+
+static void vmemmap_flush_unused_pmd(void)
+{
+ if (!unused_pmd_start)
+ return;
+ memset(__va(unused_pmd_start), PAGE_UNUSED,
+ ALIGN(unused_pmd_start, PMD_SIZE) - unused_pmd_start);
+ unused_pmd_start = 0;
+}
+
+static void __vmemmap_use_sub_pmd(unsigned long start, unsigned long end)
{
/*
* As we expect to add in the same granularity as we remove, it's
@@ -85,18 +100,41 @@ static void vmemmap_use_sub_pmd(unsigned long start, unsigned long end)
memset(__va(start), 0, sizeof(struct page));
}

+static void vmemmap_use_sub_pmd(unsigned long start, unsigned long end)
+{
+ /*
+ * We only optimize if the new used range directly follows the
+ * previously unused range (esp., when populating consecutive sections).
+ */
+ if (unused_pmd_start == start) {
+ unused_pmd_start = end;
+ if (likely(IS_ALIGNED(unused_pmd_start, PMD_SIZE)))
+ unused_pmd_start = 0;
+ return;
+ }
+ vmemmap_flush_unused_pmd();
+ __vmemmap_use_sub_pmd(start, end);
+}
+
static void vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end)
{
void *page = __va(ALIGN_DOWN(start, PMD_SIZE));

+ vmemmap_flush_unused_pmd();
+
/* Could be our memmap page is filled with PAGE_UNUSED already ... */
- vmemmap_use_sub_pmd(start, end);
+ __vmemmap_use_sub_pmd(start, end);

/* Mark the unused parts of the new memmap page PAGE_UNUSED. */
if (!IS_ALIGNED(start, PMD_SIZE))
memset(page, PAGE_UNUSED, start - __pa(page));
+ /*
+ * We want to avoid memset(PAGE_UNUSED) when populating the vmemmap of
+ * consecutive sections. Remember for the last added PMD the last
+ * unused range in the populated PMD.
+ */
if (!IS_ALIGNED(end, PMD_SIZE))
- memset(__va(end), PAGE_UNUSED, __pa(page) + PMD_SIZE - end);
+ unused_pmd_start = end;
}

/* Returns true if the PMD is completely unused and can be freed. */
@@ -104,6 +142,7 @@ static bool vmemmap_unuse_sub_pmd(unsigned long start, unsigned long end)
{
void *page = __va(ALIGN_DOWN(start, PMD_SIZE));

+ vmemmap_flush_unused_pmd();
memset(__va(start), PAGE_UNUSED, end - start);
return !memchr_inv(page, PAGE_UNUSED, PMD_SIZE);
}
--
2.26.2