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

[David Hildenbrand]

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.carst...@de.ibm.com>
Cc: Vasily Gorbik <g...@linux.ibm.com>
Cc: Christian Borntraeger <borntrae...@de.ibm.com>
Cc: Gerald Schaefer <gerald.schae...@de.ibm.com>
Signed-off-by: David Hildenbrand <da...@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