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Subject[09/17] VFALLBACK: Debugging aid
Virtual fallbacks are rare and thus subtle bugs may creep in if we do not
test the fallbacks. CONFIG_VFALLBACK_ALWAYS makes all GFP_VFALLBACK
allocations fall back to virtual mapping.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
lib/Kconfig.debug | 11 +++++++++++
mm/page_alloc.c | 9 +++++++++
2 files changed, 20 insertions(+)
Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c 2007-09-18 19:19:34.000000000 -0700
+++ linux-2.6/mm/page_alloc.c 2007-09-18 20:16:26.000000000 -0700
@@ -1205,7 +1205,16 @@ zonelist_scan:
goto this_zone_full;
}
}
+#ifdef CONFIG_VFALLBACK_ALWAYS
+ if ((gfp_mask & __GFP_VFALLBACK) &&
+ system_state == SYSTEM_RUNNING) {
+ struct page *vcompound_alloc(gfp_t, int,
+ struct zonelist *, unsigned long);

+ page = vcompound_alloc(gfp_mask, order,
+ zonelist, alloc_flags);
+ } else
+#endif
page = buffered_rmqueue(zonelist, zone, order, gfp_mask);
if (page)
break;
Index: linux-2.6/lib/Kconfig.debug
===================================================================
--- linux-2.6.orig/lib/Kconfig.debug 2007-09-18 19:19:28.000000000 -0700
+++ linux-2.6/lib/Kconfig.debug 2007-09-18 19:19:34.000000000 -0700
@@ -105,6 +105,17 @@ config DETECT_SOFTLOCKUP
can be detected via the NMI-watchdog, on platforms that
support it.)

+config VFALLBACK_ALWAYS
+ bool "Always fall back to Virtual Compound pages"
+ default y
+ help
+ Virtual compound pages are only allocated if there is no linear
+ memory available. They are a fallback and errors created by the
+ use of virtual mappings instead of linear ones may not surface
+ because of their infrequent use. This option makes every
+ allocation that allows a fallback to a virtual mapping use
+ the virtual mapping. May have a significant performance impact.
+
config SCHED_DEBUG
bool "Collect scheduler debugging info"
depends on DEBUG_KERNEL && PROC_FS
--
-
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