[RFC/PATCH v2] mm: Introduce GFP_PANIC for non-failing allocations

[Pekka Enberg <penberg@cs.helsinki.fi>]

From: Cyrill Gorcunov <gorcunov@openvz.org>

This patch introduces a GFP_PANIC flag that can be used as an annotation
that a call to kmalloc() or alloc_pages() is expected to never fail.
This is useful in early boot code, for example.

To save one GFP flag bit, use a combination of __GFP_NOFAIL,
__GFP_NOREPEAT, and __GFP_NOMEMALLOC to make sure we always end up in
the "nopage" path of the page allocator if an allocation fails.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---
Yes, this is totally untested and needs to be rebased on top of -mm.

 include/linux/gfp.h |    1 +
 mm/page_alloc.c     |    3 +++
 2 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 0bbc15f..c7c8a63 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -70,6 +70,7 @@ struct vm_area_struct;
 #define GFP_HIGHUSER_MOVABLE	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
 				 __GFP_HARDWALL | __GFP_HIGHMEM | \
 				 __GFP_MOVABLE)
+#define GFP_PANIC	(__GFP_NOFAIL | __GFP_NORETRY | __GFP_NOMEMALLOC)
 
 #ifdef CONFIG_NUMA
 #define GFP_THISNODE	(__GFP_THISNODE | __GFP_NOWARN | __GFP_NORETRY)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e2f2699..4b062e5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1670,6 +1670,9 @@ nopage:
 		dump_stack();
 		show_mem();
 	}
+	if (unlikely(gfp_mask & GFP_PANIC))
+		panic("Out of memory: %s order: %d, gfp_mask:0x%x\n",
+			p->comm, order, gfp_mask);
 got_pg:
 	return page;
 }
-- 
1.5.6.3