Re: introducing __GFP_PANIC

[Cyrill Gorcunov <gorcunov@gmail.com>]

[Cyrill Gorcunov - Mon, May 04, 2009 at 02:01:06PM +0400]
| [Pekka Enberg - Mon, May 04, 2009 at 12:57:11PM +0300]
| | On Mon, 2009-05-04 at 13:08 +0400, Cyrill Gorcunov wrote:
| | > Index: linux-2.6.git/mm/oom_kill.c
| | > =====================================================================
| | > --- linux-2.6.git.orig/mm/oom_kill.c
| | > +++ linux-2.6.git/mm/oom_kill.c
| | > @@ -422,6 +422,16 @@ static int oom_kill_process(struct task_
| | >  	return oom_kill_task(p);
| | >  }
| | >  
| | > +void oom_panic(gfp_t gfp_mask, unsigned int order)
| | > +{
| | > +	if (likely(!(gfp_mask & __GFP_PANIC)))
| | > +		return;
| | > +
| | > +	panic("Out of memory: panic due to __GFP_PANIC.\n"
| | > +		"%s order:%d, mode:0x%x\n", current->comm,
| | > +		order, gfp_mask);
| | > +}
| | 
| | I think this just makes things harder to follow. It has one call-site so
| | why not inline this there?
| | 
| 
| Indeed, will fix shortly, thanks.
| 
| 	-- Cyrill

I believe this version should be correct (still RFC).
__GFP_NOWARN has printk limit so instead of making
additional checks (while combining those prink in
original code) just adding panic with order and flags
should be cleaner (as it done at moment :)

	-- Cyrill
---
 include/linux/gfp.h |    4 +++-
 mm/failslab.c       |    3 +++
 mm/page_alloc.c     |   11 +++++++++--
 3 files changed, 15 insertions(+), 3 deletions(-)

Index: linux-2.6.git/include/linux/gfp.h
=====================================================================
--- linux-2.6.git.orig/include/linux/gfp.h
+++ linux-2.6.git/include/linux/gfp.h
@@ -58,7 +58,9 @@ struct vm_area_struct;
 #define __GFP_NOTRACK	((__force gfp_t)0)
 #endif
 
-#define __GFP_BITS_SHIFT 22	/* Room for 22 __GFP_FOO bits */
+#define __GFP_PANIC	((__force gfp_t)0x400000u) /* Panic on page alloction failure */
+
+#define __GFP_BITS_SHIFT 23	/* Room for 23 __GFP_FOO bits */
 #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
 
 /* This equals 0, but use constants in case they ever change */
Index: linux-2.6.git/mm/failslab.c
=====================================================================
--- linux-2.6.git.orig/mm/failslab.c
+++ linux-2.6.git/mm/failslab.c
@@ -17,6 +17,9 @@ bool should_failslab(size_t size, gfp_t 
 	if (gfpflags & __GFP_NOFAIL)
 		return false;
 
+	if (gfpflags & __GFP_PANIC)
+		return false;
+
         if (failslab.ignore_gfp_wait && (gfpflags & __GFP_WAIT))
 		return false;
 
Index: linux-2.6.git/mm/page_alloc.c
=====================================================================
--- linux-2.6.git.orig/mm/page_alloc.c
+++ linux-2.6.git/mm/page_alloc.c
@@ -1185,6 +1185,8 @@ static int should_fail_alloc_page(gfp_t 
 		return 0;
 	if (gfp_mask & __GFP_NOFAIL)
 		return 0;
+	if (gfp_mask & __GFP_PANIC)
+		return 0;
 	if (fail_page_alloc.ignore_gfp_highmem && (gfp_mask & __GFP_HIGHMEM))
 		return 0;
 	if (fail_page_alloc.ignore_gfp_wait && (gfp_mask & __GFP_WAIT))
@@ -1506,7 +1508,7 @@ restart:
 		 * Happens if we have an empty zonelist as a result of
 		 * GFP_THISNODE being used on a memoryless node
 		 */
-		return NULL;
+		goto nopage;
 	}
 
 	page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
@@ -1685,7 +1687,12 @@ nopage:
 		dump_stack();
 		show_mem();
 	}
-	return page;
+	if (unlikely((gfp_mask & __GFP_PANIC))) {
+		panic("Out of memory: panic due to __GFP_PANIC.\n"
+			"%s order:%d, mode:0x%x\n", p->comm,
+			order, gfp_mask);
+	}
+	return NULL;
 got_pg:
 	if (kmemcheck_enabled)
 		kmemcheck_pagealloc_alloc(page, order, gfp_mask);