introducing __GFP_PANIC

[Cyrill Gorcunov <gorcunov@gmail.com>]

[Pekka Enberg - Sun, May 03, 2009 at 07:54:38PM +0300]
...
| > | I don't like this approach because you'd need to do a kzalloc_panic()
| > | and so on for it to be truly useful. What's wrong with adding a
| > | __GFP_PANIC check in __alloc_pages_internal() (or whatever it's called
| > | in -mm now) next to __GFP_NOWARN?
| > |
| > |                       Pekka
| > |
| >
| > Hi Pekka,
| >
| > ufortunatelly __alloc_pages_internal is not the only place where
| > we do return NULL from kmalloc. As example - failslab facility
| > (in slab_alloc call). Anyway -- I'll take a closer look.
| 
| Right. I think failslab needs some fixing _not_ to return NULL if
| __GFP_PANIC is set.
| 

Ok, as a first raw draft (_not_ covering all the cases) it could
be something like this. It touches only __alloc_pages_internal
and we have to bespread as well:

1) alloc_pages with order >= MAX_ORDER (gfp.h)
2) the same for alloc_pages_node (both used by SLOB)
3) all __kmalloc should be explored as well.
4) ???

Anyway -- take a look on __alloc_pages_internal part :)

	-- Cyrill

---
 include/linux/gfp.h |    4 +++-
 mm/page_alloc.c     |    8 +++++---
 2 files changed, 8 insertions(+), 4 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/page_alloc.c
=====================================================================
--- linux-2.6.git.orig/mm/page_alloc.c
+++ linux-2.6.git/mm/page_alloc.c
@@ -1496,7 +1496,7 @@ __alloc_pages_internal(gfp_t gfp_mask, u
 	might_sleep_if(wait);
 
 	if (should_fail_alloc_page(gfp_mask, order))
-		return NULL;
+		goto nopage;
 
 restart:
 	z = zonelist->_zonerefs;  /* the list of zones suitable for gfp_mask */
@@ -1506,7 +1506,7 @@ 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 +1685,9 @@ nopage:
 		dump_stack();
 		show_mem();
 	}
-	return page;
+	if (unlikely(gfp_mask & __GFP_PANIC))
+		panic("Out of memory: panic due to __GFP_PANIC\n");
+	return NULL;
 got_pg:
 	if (kmemcheck_enabled)
 		kmemcheck_pagealloc_alloc(page, order, gfp_mask);