introducing __GFP_PANIC

Cyrill Gorcunov
2009-05-03T17:23:50Z

[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);