Re: [PATCH] mm/page_alloc.c: drop dead destroy_compound_page()

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 10 Jan 2015 02:41:43 +0200 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> On Fri, Jan 09, 2015 at 04:24:19PM -0800, Andrew Morton wrote:
> > On Thu,  8 Jan 2015 16:10:04 +0200 (EET) "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:
> > 
> > > Something like this?
> > > 
> > > >From 5fd481c1c521112e9cea407f5a2644c9f93d0e14 Mon Sep 17 00:00:00 2001
> > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > > Date: Thu, 8 Jan 2015 15:59:23 +0200
> > > Subject: [PATCH] mm: more checks on free_pages_prepare() for tail pages
> > > 
> > > Apart form being dead, destroy_compound_page() did some potentially
> > > useful checks. Let's re-introduce them in free_pages_prepare(), where
> > > they can be acctually triggered.
> > > 
> > > compound_order() assert is already in free_pages_prepare(). We have few
> > > checks for tail pages left.
> > > 
> > 
> > I'm thinking we avoid the overhead unless CONFIG_DEBUG_VM?
> 
> That's why there's "if (!IS_ENABLED(CONFIG_DEBUG_VM))". Is it wrong in
> some way?
> I didn't check, but I assume compiler is smart enough to get rid of
> free_tail_pages_check() if CONFIG_DEBUG_VM is not defined. No?

doh, OK.  I updated the
mm-more-checks-on-free_pages_prepare-for-tail-pages.patch changelog to
reflect this and did

--- a/mm/page_alloc.c~mm-more-checks-on-free_pages_prepare-for-tail-pages-fix
+++ a/mm/page_alloc.c
@@ -764,19 +764,18 @@ static void free_one_page(struct zone *z
 	spin_unlock(&zone->lock);
 }
 
-static int free_tail_pages_check(struct page *head_page, struct page *page)
+static void free_tail_pages_check(struct page *head_page, struct page *page)
 {
 	if (!IS_ENABLED(CONFIG_DEBUG_VM))
-		return 0;
+		return;
 	if (unlikely(!PageTail(page))) {
 		bad_page(page, "PageTail not set", 0);
-		return 1;
+		return;
 	}
 	if (unlikely(page->first_page != head_page)) {
 		bad_page(page, "first_page not consistent", 0);
-		return 1;
+		return;
 	}
-	return 0;
 }
 
 static bool free_pages_prepare(struct page *page, unsigned int order)
_

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