[PATCH V2 1/2] ARM: remove unnecessary flush of anon pages in flush_dcache_page()

[Simon Baatz]

On non-aliasing VIPT D-caches, there is no need to flush the kernel
mapping of anon pages in flush_dcache_page() directly.  If the page is
mapped as executable later, the necessary D/I-cache flush will be done
in __sync_icache_dcache().

Signed-off-by: Simon Baatz <gmbnomis at gmail.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Russell King <linux at arm.linux.org.uk>
---

Changes:

in V2:
- Followed Catalin's suggestion to reverse the order of the patches
- Clarified comment for flush_dcache_page()


 arch/arm/mm/flush.c |   45 ++++++++++++++++++++++++++-------------------
 1 file changed, 26 insertions(+), 19 deletions(-)

diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index 40ca11e..5c474a1 100644
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -257,16 +257,20 @@ void __sync_icache_dcache(pte_t pteval)
  * of this page.
  *
  * We have three cases to consider:
- *  - VIPT non-aliasing cache: fully coherent so nothing required.
- *  - VIVT: fully aliasing, so we need to handle every alias in our
- *          current VM view.
- *  - VIPT aliasing: need to handle one alias in our current VM view.
+ *  - VIPT non-aliasing D-cache:
+ *          D-cache: fully coherent so nothing required.
+ *          I-cache: Ensure I/D coherency in case of an already mapped page;
+ *                   __sync_icache_dcache() will handle the other cases.
+ *  - VIPT aliasing D-cache:
+ *          D-cache: need to handle one alias in our current VM view.
+ *          I-cache: same as VIPT non-aliasing cache.
+ *  - VIVT D-cache: fully aliasing, so we need to handle every alias in our
+ *                  current VM view.
  *
- * If we need to handle aliasing:
- *  If the page only exists in the page cache and there are no user
- *  space mappings, we can be lazy and remember that we may have dirty
- *  kernel cache lines for later.  Otherwise, we assume we have
- *  aliasing mappings.
+ * If the page only exists in the page cache and there are no user
+ * space mappings, we can be lazy and remember that we may have dirty
+ * kernel cache lines for later.  Otherwise, we assume we have
+ * aliasing mappings.
  *
  * Note that we disable the lazy flush for SMP configurations where
  * the cache maintenance operations are not automatically broadcasted.
@@ -284,17 +288,20 @@ void flush_dcache_page(struct page *page)
 
 	mapping = page_mapping(page);
 
-	if (!cache_ops_need_broadcast() &&
-	    mapping && !mapping_mapped(mapping))
-		clear_bit(PG_dcache_clean, &page->flags);
-	else {
-		__flush_dcache_page(mapping, page);
-		if (mapping && cache_is_vivt())
-			__flush_dcache_aliases(mapping, page);
-		else if (mapping)
-			__flush_icache_all();
-		set_bit(PG_dcache_clean, &page->flags);
+	if (!cache_ops_need_broadcast()) {
+		if ((mapping && !mapping_mapped(mapping)) ||
+		    (!mapping && cache_is_vipt_nonaliasing())) {
+			clear_bit(PG_dcache_clean, &page->flags);
+			return;
+		}
 	}
+
+	__flush_dcache_page(mapping, page);
+	if (mapping && cache_is_vivt())
+		__flush_dcache_aliases(mapping, page);
+	else if (mapping)
+		__flush_icache_all();
+	set_bit(PG_dcache_clean, &page->flags);
 }
 EXPORT_SYMBOL(flush_dcache_page);
 
-- 
1.7.9.5