From fa5ec8a1f66f3c2a3af723abcf8085509c9ee682 Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Tue, 7 Jul 2009 00:14:14 -0700 Subject: slub: add option to disable higher order debugging slabs When debugging is enabled, slub requires that additional metadata be stored in slabs for certain options: SLAB_RED_ZONE, SLAB_POISON, and SLAB_STORE_USER. Consequently, it may require that the minimum possible slab order needed to allocate a single object be greater when using these options. The most notable example is for objects that are PAGE_SIZE bytes in size. Higher minimum slab orders may cause page allocation failures when oom or under heavy fragmentation. This patch adds a new slub_debug option, which disables debugging by default for caches that would have resulted in higher minimum orders: slub_debug=O When this option is used on systems with 4K pages, kmalloc-4096, for example, will not have debugging enabled by default even if CONFIG_SLUB_DEBUG_ON is defined because it would have resulted in a order-1 minimum slab order. Reported-by: Larry Finger Tested-by: Larry Finger Cc: Christoph Lameter Signed-off-by: David Rientjes Signed-off-by: Pekka Enberg --- Documentation/vm/slub.txt | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'Documentation') diff --git a/Documentation/vm/slub.txt b/Documentation/vm/slub.txt index bb1f5c6e28b..510917ff59e 100644 --- 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) + O Switch debugging off for caches that would have + caused higher minimum slab orders - Switch all debugging off (useful if the kernel is configured with CONFIG_SLUB_DEBUG_ON) @@ -59,6 +61,14 @@ to the dentry cache with slub_debug=F,dentry +Debugging options may require the minimum possible slab order to increase as +a result of storing the metadata (for example, caches with PAGE_SIZE object +sizes). This has a higher liklihood of resulting in slab allocation errors +in low memory situations or if there's high fragmentation of memory. To +switch off debugging for such caches by default, use + + slub_debug=O + In case you forgot to enable debugging on the kernel command line: It is possible to enable debugging manually when the kernel is up. Look at the contents of: -- cgit v1.2.3-70-g09d2