linux-kernel - [RFC 0/2] add static key for slub

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Date:   Thu,  4 Apr 2019 11:15:29 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     linux-mm@...ck.org
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Subject: [RFC 0/2] add static key for slub_debug

Hi,

I looked a bit at SLUB debugging capabilities and first thing I noticed is
there's no static key guarding the runtime enablement as is common for similar
debugging functionalities, so here's a RFC to add it. Can be further improved
if there's interest.

It's true that in the alloc fast path the debugging check overhead is AFAICS
amortized by the per-cpu cache, i.e. when the allocation is from there, no
debugging functionality is performed. IMHO that's kinda a weakness, especially
for SLAB_STORE_USER, so I might also look at doing something about it, and then
the static key might be more critical for overhead reduction.

In the freeing fast path I quickly checked the stats and it seems that in
do_slab_free(), the "if (likely(page == c->page))" is not as likely as it
declares, as in the majority of cases, freeing doesn't happen on the object
that belongs to the page currently cached. So the advantage of a static key in
slow path __slab_free() should be more useful immediately.

Vlastimil Babka (2):
  mm, slub: introduce static key for slub_debug
  mm, slub: add missing kmem_cache_debug() checks

 mm/slub.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

-- 
2.21.0