On Thu, Jun 21, 2018 at 8:01 AM Michal Hocko mhocko@kernel.org wrote:
On Thu 21-06-18 01:15:30, Cristopher Lameter wrote:
On Wed, 20 Jun 2018, Shakeel Butt wrote:
For !CONFIG_SLUB_DEBUG, SLUB does not maintain the number of slabs allocated per node for a kmem_cache. Thus, slabs_node() in __kmem_cache_empty(), __kmem_cache_shrink() and __kmem_cache_destroy() will always return 0 for such config. This is wrong and can cause issues for all users of these functions.
CONFIG_SLUB_DEBUG is set by default on almost all builds. The only case where CONFIG_SLUB_DEBUG is switched off is when we absolutely need to use the minimum amount of memory (embedded or some such thing).
I thought those would be using SLOB rather than SLUB.
The right solution is to make slabs_node() work even for !CONFIG_SLUB_DEBUG. The commit 0f389ec63077 ("slub: No need for per node slab counters if !SLUB_DEBUG") had put the per node slab counter under CONFIG_SLUB_DEBUG because it was only read through sysfs API and the sysfs API was disabled on !CONFIG_SLUB_DEBUG. However the users of the per node slab counter assumed that it will work in the absence of CONFIG_SLUB_DEBUG. So, make the counter work for !CONFIG_SLUB_DEBUG.
Please do not do this. Find a way to avoid these checks. The objective of a !CONFIG_SLUB_DEBUG configuration is to not compile in debuggin checks etc etc in order to reduce the code/data footprint to the minimum necessary while sacrificing debuggability etc etc.
Maybe make it impossible to disable CONFIG_SLUB_DEBUG if CGROUPs are in use?
Why don't we simply remove the config option altogether and make it enabled effectively.
Christopher, how do you want to proceed? I don't have any strong opinion. I just don't want KASAN users kept broken for SLUB.
thanks, Shakeel