SLUB: support slub_debug on by default

Add a new configuration variable

CONFIG_SLUB_DEBUG_ON

If set then the kernel will be booted by default with slab debugging
switched on. Similar to CONFIG_SLAB_DEBUG. By default slab debugging
is available but must be enabled by specifying "slub_debug" as a
kernel parameter.

Also add support to switch off slab debugging for a kernel that was
built with CONFIG_SLUB_DEBUG_ON. This works by specifying

slub_debug=-

as a kernel parameter.

Dave Jones wanted this feature.
http://marc.info/?l=linux-kernel&m=118072189913045&w=2

[akpm@linux-foundation.org: clean up switch statement]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4344f69..8916410 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1580,35 +1580,39 @@ and is between 256 and 4096 characters. It is defined in the file
 
        slram=          [HW,MTD]
 
-       slub_debug      [MM, SLUB]
-                       Enabling slub_debug allows one to determine the culprit
-                       if slab objects become corrupted. Enabling slub_debug
-                       creates guard zones around objects and poisons objects
-                       when not in use. Also tracks the last alloc / free.
-                       For more information see Documentation/vm/slub.txt.
+       slub_debug[=options[,slabs]]    [MM, SLUB]
+                       Enabling slub_debug allows one to determine the
+                       culprit if slab objects become corrupted. Enabling
+                       slub_debug can create guard zones around objects and
+                       may poison objects when not in use. Also tracks the
+                       last alloc / free. For more information see
+                       Documentation/vm/slub.txt.
 
        slub_max_order= [MM, SLUB]
-                       Determines the maximum allowed order for slabs. Setting
-                       this too high may cause fragmentation.
-                       For more information see Documentation/vm/slub.txt.
+                       Determines the maximum allowed order for slabs.
+                       A high setting may cause OOMs due to memory
+                       fragmentation. For more information see
+                       Documentation/vm/slub.txt.
 
        slub_min_objects=       [MM, SLUB]
-                       The minimum objects per slab. SLUB will increase the
-                       slab order up to slub_max_order to generate a
-                       sufficiently big slab to satisfy the number of objects.
-                       The higher the number of objects the smaller the overhead
-                       of tracking slabs.
+                       The minimum number of objects per slab. SLUB will
+                       increase the slab order up to slub_max_order to
+                       generate a sufficiently large slab able to contain
+                       the number of objects indicated. The higher the number
+                       of objects the smaller the overhead of tracking slabs
+                       and the less frequently locks need to be acquired.
                        For more information see Documentation/vm/slub.txt.
 
        slub_min_order= [MM, SLUB]
                        Determines the mininum page order for slabs. Must be
-                       lower than slub_max_order
+                       lower than slub_max_order.
                        For more information see Documentation/vm/slub.txt.
 
        slub_nomerge    [MM, SLUB]
-                       Disable merging of slabs of similar size. May be
+                       Disable merging of slabs with similar size. May be
                        necessary if there is some reason to distinguish
-                       allocs to different slabs.
+                       allocs to different slabs. Debug options disable
+                       merging on their own.
                        For more information see Documentation/vm/slub.txt.
 
        smart2=         [HW]

diff --git a/Documentation/vm/slub.txt b/Documentation/vm/slub.txt
index 1523320..df812b0 100644 (file)
--- a/Documentation/vm/slub.txt
+++ b/Documentation/vm/slub.txt
@@ -41,6 +41,8 @@ Possible debug options are
        P               Poisoning (object and padding)
        U               User tracking (free and alloc)
        T               Trace (please only use on single slabs)
+       -               Switch all debugging off (useful if the kernel is
+                       configured with CONFIG_SLUB_DEBUG_ON)
 
 F.e. in order to boot just with sanity checks and red zoning one would specify:
 

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index fab32a2..6408440 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -152,6 +152,19 @@ config DEBUG_SLAB_LEAK
        bool "Memory leak debugging"
        depends on DEBUG_SLAB
 
+config SLUB_DEBUG_ON
+       bool "SLUB debugging on by default"
+       depends on SLUB && SLUB_DEBUG
+       default n
+       help
+         Boot with debugging on by default. SLUB boots by default with
+         the runtime debug capabilities switched off. Enabling this is
+         equivalent to specifying the "slub_debug" parameter on boot.
+         There is no support for more fine grained debug control like
+         possible with slub_debug=xxx. SLUB debugging may be switched
+         off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying
+         "slub_debug=-".
+
 config DEBUG_PREEMPT
        bool "Debug preemptible kernel"
        depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT

diff --cc mm/slub.c
Simple merge