From: Zhaoyang Huang <[email protected]>
Double times of clear_page observed in an arm SOC(A55) when
CONFIG_INIT_ON_ALLOC_DEFAULT_ON is on, which introduced by
vma_alloc_zeroed_movable_folio within do_anonymous_pages.
Since there is no D-cache operation within v6's clear_user_highpage,
I would like to suggest to remove the redundant clear_page.
struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
unsigned long vaddr)
{
struct folio *folio;
//first clear_page invoked by vma_alloc_folio==>alloc_page==>post_alloc_hook
folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr, false);
if (folio)
//second clear_page which is meaningless since it do nothing to D-cache in armv6
clear_user_highpage(&folio->page, vaddr);
return folio;
}
PS:
Here are all positions called clear_user_highpage which are paired
with alloc_pages. IMO, it is safe to skip the second clear_page under
armv6.
drivers/media/v4l2-core/videobuf-dma-sg.c:441:
clear_user_highpage(page, vmf->address);
fs/dax.c:1612: clear_user_highpage(vmf->cow_page, vmf->address);
include/linux/highmem.h:231: clear_user_highpage(&folio->page, vaddr);
mm/memory.c:5974: clear_user_highpage(p, addr + i * PAGE_SIZE);
mm/memory.c:5982: clear_user_highpage(page + idx, addr);
mm/shmem.c:2621: clear_user_highpage(&folio->page, dst_addr);
mm/khugepaged.c:796: clear_user_highpage(page, _address);
Signed-off-by: Zhaoyang Huang <[email protected]>
---
arch/arm/mm/copypage-v6.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/arm/mm/copypage-v6.c b/arch/arm/mm/copypage-v6.c
index a1a71f36d850..6f8bee1b3203 100644
--- a/arch/arm/mm/copypage-v6.c
+++ b/arch/arm/mm/copypage-v6.c
@@ -9,6 +9,7 @@
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
+#include <linux/gfp.h>
#include <asm/shmparam.h>
#include <asm/tlbflush.h>
@@ -45,6 +46,13 @@ static void v6_copy_user_highpage_nonaliasing(struct page *to,
*/
static void v6_clear_user_highpage_nonaliasing(struct page *page, unsigned long vaddr)
{
+ /*
+ * This criteria only help bailing out when CONFIG_INIT_ON_ALLOC_DEFAULT_ON
+ * is on. The page has been memset to zero when it allocated and the
+ * bellowing clear_page will do it again.
+ */
+ if (want_init_on_alloc(GFP_HIGHUSER_MOVABLE))
+ return;
void *kaddr = kmap_atomic(page);
clear_page(kaddr);
kunmap_atomic(kaddr);
--
2.25.1