mm-highmem-makes-flush_all_zero_pkmaps-return-index-of-last-flushed-entry-v2

In current code, after flush_all_zero_pkmaps() is invoked,
then re-iterate all pkmaps. It can be optimized if flush_all_zero_pkmaps()
return index of first flushed entry. With this index,
we can immediately map highmem page to virtual address represented by index.
So change return type of flush_all_zero_pkmaps()
and return index of first flushed entry.

Additionally, update last_pkmap_nr to this index.
It is certain that entry which is below this index is occupied by other mapping,
therefore updating last_pkmap_nr to this index is reasonable optimization.

Signed-off-by: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 0683869d6a70e9c7964be3aa37f513e1a7797cbb..97ad208d91ccfd15e92265455b4356949081e8d1 100644 (file)
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -32,7 +32,7 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
 
 #ifdef CONFIG_HIGHMEM
 #include <asm/highmem.h>
-#define PKMAP_INDEX_INVAL (-1)
+#define PKMAP_INVALID_INDEX (LAST_PKMAP)
 
 /* declarations for linux/mm/highmem.c */
 unsigned int nr_free_highpages(void);

diff --git a/mm/highmem.c b/mm/highmem.c
index 264a00a9ccf328b60cfe25befaac5adafe1dcb28..91e80022aaad72a5c1ccb3b784ec19bd841d17a0 100644 (file)
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -107,10 +107,10 @@ struct page *kmap_to_page(void *vaddr)
 }
 EXPORT_SYMBOL(kmap_to_page);
 
-static int flush_all_zero_pkmaps(void)
+static unsigned int flush_all_zero_pkmaps(void)
 {
        int i;
-       int index = PKMAP_INDEX_INVAL;
+       unsigned int index = PKMAP_INVALID_INDEX;
 
        flush_cache_kmaps();
 
@@ -142,9 +142,10 @@ static int flush_all_zero_pkmaps(void)
                          &pkmap_page_table[i]);
 
                set_page_address(page, NULL);
-               index = i;
+               if (index == PKMAP_INVALID_INDEX)
+                       index = i;
        }
-       if (index != PKMAP_INDEX_INVAL)
+       if (index != PKMAP_INVALID_INDEX)
                flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 
        return index;
@@ -155,15 +156,19 @@ static int flush_all_zero_pkmaps(void)
  */
 void kmap_flush_unused(void)
 {
+       unsigned int index;
+
        lock_kmap();
-       flush_all_zero_pkmaps();
+       index = flush_all_zero_pkmaps();
+       if (index != PKMAP_INVALID_INDEX && (index < last_pkmap_nr))
+               last_pkmap_nr = index;
        unlock_kmap();
 }
 
 static inline unsigned long map_new_virtual(struct page *page)
 {
        unsigned long vaddr;
-       int index = PKMAP_INDEX_INVAL;
+       unsigned int index = PKMAP_INVALID_INDEX;
        int count;
 
 start:
@@ -173,8 +178,7 @@ start:
                last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
                if (!last_pkmap_nr) {
                        index = flush_all_zero_pkmaps();
-                       if (index != PKMAP_INDEX_INVAL)
-                               break; /* Found a usable entry */
+                       break;
                }
                if (!pkmap_count[last_pkmap_nr]) {
                        index = last_pkmap_nr;
@@ -187,7 +191,7 @@ start:
        /*
         * Sleep for somebody else to unmap their entries
         */
-       if (index == PKMAP_INDEX_INVAL) {
+       if (index == PKMAP_INVALID_INDEX) {
                DECLARE_WAITQUEUE(wait, current);
 
                __set_current_state(TASK_UNINTERRUPTIBLE);
@@ -211,6 +215,7 @@ start:
                   &(pkmap_page_table[index]), mk_pte(page, kmap_prot));
 
        pkmap_count[index] = 1;
+       last_pkmap_nr = index;
        set_page_address(page, (void *)vaddr);
 
        return vaddr;
@@ -332,6 +337,7 @@ struct page_address_map {
        void *virtual;
        struct list_head list;
 };
+
 static struct page_address_map page_address_maps[LAST_PKMAP];
 
 /*