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 --- mm/slub.c | 41 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 38 insertions(+), 3 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index a9201d83178b..466089cd5deb 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -141,6 +141,13 @@ #define DEBUG_DEFAULT_FLAGS (SLAB_DEBUG_FREE | SLAB_RED_ZONE | \ SLAB_POISON | SLAB_STORE_USER) +/* + * Debugging flags that require metadata to be stored in the slab, up to + * DEBUG_SIZE in size. + */ +#define DEBUG_SIZE_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER) +#define DEBUG_SIZE (3 * sizeof(void *) + 2 * sizeof(struct track)) + /* * Set of flags that will prevent slab merging */ @@ -326,6 +333,7 @@ static int slub_debug; #endif static char *slub_debug_slabs; +static int disable_higher_order_debug; /* * Object debugging @@ -977,6 +985,15 @@ static int __init setup_slub_debug(char *str) */ goto check_slabs; + if (tolower(*str) == 'o') { + /* + * Avoid enabling debugging on caches if its minimum order + * would increase as a result. + */ + disable_higher_order_debug = 1; + goto out; + } + slub_debug = 0; if (*str == '-') /* @@ -1023,13 +1040,27 @@ static unsigned long kmem_cache_flags(unsigned long objsize, unsigned long flags, const char *name, void (*ctor)(void *)) { + int debug_flags = slub_debug; + /* * Enable debugging if selected on the kernel commandline. */ - if (slub_debug && (!slub_debug_slabs || - strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs)) == 0)) - flags |= slub_debug; + if (debug_flags) { + if (slub_debug_slabs && + strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs))) + goto out; + + /* + * Disable debugging that increases slab size if the minimum + * slab order would have increased as a result. + */ + if (disable_higher_order_debug && + get_order(objsize + DEBUG_SIZE) > get_order(objsize)) + debug_flags &= ~DEBUG_SIZE_FLAGS; + flags |= debug_flags; + } +out: return flags; } #else @@ -1561,6 +1592,10 @@ slab_out_of_memory(struct kmem_cache *s, gfp_t gfpflags, int nid) "default order: %d, min order: %d\n", s->name, s->objsize, s->size, oo_order(s->oo), oo_order(s->min)); + if (oo_order(s->min) > get_order(s->objsize)) + printk(KERN_WARNING " %s debugging increased min order, use " + "slub_debug=O to disable.\n", s->name); + for_each_online_node(node) { struct kmem_cache_node *n = get_node(s, node); unsigned long nr_slabs; -- cgit v1.2.3-55-g7522