[Devel] [PATCH rh7] x86: arch_free_page() introduced

[Vladimir Davydov]

On Tue, Nov 17, 2015 at 03:42:46PM +0100, Stanislav Kinsburskiy wrote:
> 
> 
> 17.11.2015 15:20, Vladimir Davydov пишет:
> >On Thu, Nov 12, 2015 at 10:01:14PM +0400, Stanislav Kinsburskiy wrote:
> >
> >>@@ -0,0 +1,23 @@
> >>+#ifndef _ASM_X86_FREE_PAGE_H
> >>+#define _ASM_X86_FREE_PAGE_H
> >>+
> >>+#ifdef __KERNEL__
> >>+
> >>+#ifndef __ASSEMBLY__
> >>+
> >>+#include <linux/jump_label.h>
> >>+
> >>+#define HAVE_ARCH_FREE_PAGE
> >>+
> >>+extern struct static_key zero_free_pages;
> >>+extern void do_zero_pages(struct page *page, int order);
> >>+
> >>+static __always_inline void arch_free_page(struct page *page, int order)
> >>+{
> >>+	if (static_key_false(&zero_free_pages))
> >>+		do_zero_pages(page, order);
> >>+}
> >There is no point in making this feature arch-dependant now, as you use
> >jump labels, which are arch-independent. The only reason why I had to
> >overwrite arch_free_page in PCS6 is that I had to write some asm code to
> >implement functionality close to that provided by jump labels, which are
> >absent in RH6-based kernels. Please move it to mm/page_alloc.c.
> >
> >Thanks.
> 
> If we will make this function generic, then we have to declare
> "zero_free_pages" as generic (which is more or less ok)  and define
> do_zero_pages for the case, when HAVE_ARCH_FREE_PAGE is not defined. Does
> the goal worth it?
> If yes, then why?
> 

I don't think I get your point. All I want you to do is something like
this:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f70c5f4da2a2..12126f212f3b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -730,8 +730,11 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 
 	if (PageAnon(page))
 		page->mapping = NULL;
-	for (i = 0; i < (1 << order); i++)
+	for (i = 0; i < (1 << order); i++) {
 		bad += free_pages_check(page + i);
+		if (static_key_false(&zero_free_pages))
+			clear_highpage(page + i);
+	}
 	if (bad)
 		return false;

IMO this is better than messing around arch code.