Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

From: Yang Shi
Date: Mon Oct 09 2017 - 17:01:08 EST




On 10/9/17 11:53 AM, Yang Shi wrote:


On 10/8/17 11:36 PM, Michal Hocko wrote:
On Mon 09-10-17 08:33:16, Michal Hocko wrote:
On Sat 07-10-17 00:37:55, Yang Shi wrote:


On 10/6/17 2:37 AM, Michal Hocko wrote:
On Thu 05-10-17 05:29:10, Yang Shi wrote:
[...]
+ list_for_each_entry_safe(s, s2, &slab_caches, list) {
+ if (!is_root_cache(s) || (s->flags & SLAB_RECLAIM_ACCOUNT))
+ continue;
+
+ memset(&sinfo, 0, sizeof(sinfo));

why do you zero out the structure. All the fields you are printing are
filled out in get_slabinfo.

No special reason, just wipe out the potential stale data on the stack.

Do not add code that has no meaning. The OOM killer is a slow path but
that doesn't mean we should throw spare cycles out of the window.

With this fixed and the compile fix [1] folded, feel free to add my
Acked-by: Michal Hocko <mhocko@xxxxxxxx>

[1] http://lkml.kernel.org/r/1507492085-42264-1-git-send-email-yang.s@xxxxxxxxxxxxxxx

Did some more thorough test and took the code a little deeper, it sounds !CONFIG_SLOB is not enough. Some data structure and functions depends on CONFIG_SLUB_DEBUG, i.e. kmem_cache_node->total_objects and node_nr_objs(), which are essential of get_slabinfo().

So, I'm supposed it makes more sense to protect the related slab stats code and the unreclaimable slabinfo dump with CONFIG_SLAB || CONFIG_SLUB_DEBUG.

This is needed to solve compile error when CONFIG_SLUB && !CONFIG_SLUB_DEBUG

Yang


Thanks,
Yang