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From: Catalin Marinas <catalin.marinas@arm.com>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@kernel.org>,
	Matthew Wilcox <willy@infradead.org>, Qian Cai <cai@lca.pw>
Subject: Re: [PATCH v3 1/3] mm: kmemleak: Make the tool tolerant to struct scan_area allocation failures
Date: Mon, 7 Oct 2019 10:56:58 +0100	[thread overview]
Message-ID: <20191007095658.GF45043@arrakis.emea.arm.com> (raw)
In-Reply-To: <ba47fb68-f44c-04c9-7ea8-2705e799937b@ozlabs.ru>

On Sat, Oct 05, 2019 at 01:08:43PM +1000, Alexey Kardashevskiy wrote:
> On 03/10/2019 18:41, Catalin Marinas wrote:
> > On Thu, Oct 03, 2019 at 04:13:07PM +1000, Alexey Kardashevskiy wrote:
> >> On 13/08/2019 02:06, Catalin Marinas wrote:
> >>> Object scan areas are an optimisation aimed to decrease the false
> >>> positives and slightly improve the scanning time of large objects known
> >>> to only have a few specific pointers. If a struct scan_area fails to
> >>> allocate, kmemleak can still function normally by scanning the full
> >>> object.
> >>>
> >>> Introduce an OBJECT_FULL_SCAN flag and mark objects as such when
> >>> scan_area allocation fails.
> >>
> >> I came across this one while bisecting sudden drop in throughput of a
> >> 100Gbit Mellanox CX4 ethernet card in a PPC POWER9 system, the speed
> >> dropped from 100Gbit to about 40Gbit. Bisect pointed at dba82d943177,
> >> this are the relevant config options:
> >>
> >> [fstn1-p1 kernel]$ grep KMEMLEAK ~/pbuild/kernel-le-4g/.config
> >> CONFIG_HAVE_DEBUG_KMEMLEAK=y
> >> CONFIG_DEBUG_KMEMLEAK=y
> >> CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE=16000
> >> # CONFIG_DEBUG_KMEMLEAK_TEST is not set
> >> # CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF is not set
> >> CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN=y
> > 
> > The throughput drop is probably caused caused by kmemleak slowing down
> > all memory allocations (including skb). So that's expected. You may get
> > similar drop with other debug options like lock proving, kasan.
> 
> I was not precise. I meant that before dba82d943177 kmemleak would
> work but would not slow network down (at least 100Gbit) and now it
> does which is downgrade so I was wondering if kmemleak just got so
> much better to justify this change or there is a bug somewhere, so
> which one is it? Or "LOG_SIZE=400" never really worked?

I suspect LOG_SIZE=400 never worked on your system (you can check the
log for any kmemleak disabled messages).

Thanks for testing the patch.

-- 
Catalin


  parent reply	other threads:[~2019-10-07  9:57 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-12 16:06 [PATCH v3 0/3] mm: kmemleak: Use a memory pool for kmemleak object allocations Catalin Marinas
2019-08-12 16:06 ` [PATCH v3 1/3] mm: kmemleak: Make the tool tolerant to struct scan_area allocation failures Catalin Marinas
     [not found]   ` <2ac37341-097e-17a2-fb6b-7912da9fa38e@ozlabs.ru>
2019-10-03  8:41     ` Catalin Marinas
     [not found]       ` <ba47fb68-f44c-04c9-7ea8-2705e799937b@ozlabs.ru>
2019-10-07  9:56         ` Catalin Marinas [this message]
2019-08-12 16:06 ` [PATCH v3 2/3] mm: kmemleak: Simple memory allocation pool for kmemleak objects Catalin Marinas
2019-08-13  9:37   ` Catalin Marinas
2019-08-12 16:06 ` [PATCH v3 3/3] mm: kmemleak: Use the memory pool for early allocations Catalin Marinas
2019-08-13  9:35   ` Catalin Marinas
2019-08-13 12:35   ` Qian Cai
2019-08-13 13:49     ` Catalin Marinas
2019-08-12 21:07 ` [PATCH v3 0/3] mm: kmemleak: Use a memory pool for kmemleak object allocations Andrew Morton
2019-08-13  9:40   ` Catalin Marinas
2019-12-03 15:51 ` Noam Stolero
2019-12-03 16:08   ` Catalin Marinas
2019-12-05 16:16     ` Noam Stolero

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