linux-kernel - Re: [PATCH v2] mm/slub: disable user tracing for kmemleak caches by default

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Message-ID: <ef5c2539-735-42ef-89e0-ef142da415cd@google.com>
Date:   Fri, 15 Jan 2021 11:41:07 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Johannes Berg <johannes@...solutions.net>
cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH v2] mm/slub: disable user tracing for kmemleak caches by
 default

On Wed, 13 Jan 2021, Johannes Berg wrote:

> From: Johannes Berg <johannes.berg@...el.com>
> 
> If kmemleak is enabled, it uses a kmem cache for its own objects.
> These objects are used to hold information kmemleak uses, including
> a stack trace. If slub_debug is also turned on, each of them has
> *another* stack trace, so the overhead adds up, and on my tests (on
> ARCH=um, admittedly) 2/3rds of the allocations end up being doing
> the stack tracing.
> 
> Turn off SLAB_STORE_USER if SLAB_NOLEAKTRACE was given, to avoid
> storing the essentially same data twice.
> 
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>

Acked-by: David Rientjes <rientjes@...gle.com>

> ---
> Perhaps instead it should go the other way around, and kmemleak
> could even use/access the stack trace that's already in there ...
> But I don't really care too much, I can just turn off slub debug
> for the kmemleak caches via the command line anyway :-)
> 

I think making the change to kmem_cache_flags() is likely the simplest.