From: Andrew Morton <akpm@linux-foundation.org>
To: Richard Yao <ryao@gentoo.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Zhang Yanfei <zhangyanfei.yes@gmail.com>,
Wanpeng Li <liwanp@linux.vnet.ibm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel@gentoo.org, Matthew Thode <mthode@mthode.org>
Subject: Re: [PATCH] mm/vmalloc: Introduce DEBUG_VMALLOCINFO to reduce spinlock contention
Date: Thu, 17 Apr 2014 16:18:28 -0700 [thread overview]
Message-ID: <20140417161828.b1740b30bf9d5462f46562cc@linux-foundation.org> (raw)
In-Reply-To: <1397148058-8737-1-git-send-email-ryao@gentoo.org>
On Thu, 10 Apr 2014 12:40:58 -0400 Richard Yao <ryao@gentoo.org> wrote:
> Performance analysis of software compilation by Gentoo portage on an
> Intel E5-2620 with 64GB of RAM revealed that a sizeable amount of time,
> anywhere from 5% to 15%, was spent in get_vmalloc_info(), with at least
> 40% of that time spent in the _raw_spin_lock() invoked by it.
This means that something in userspace is beating the crap out of
/proc/meminfo. What is it and why is it doing this?
/proc/meminfo reads a large amount of stuff and gathering it will
always be expensive. I don't think we really want to be doing
significant work and adding significant complexity to optimize meminfo.
If there really is a legitimate need to be reading meminfo with this
frequency then it would be pretty simple to optimise
get_vmalloc_info(): all it does is to return two ulongs and we could
maintain those at vmalloc/vfree time rather than doing the big list
walk.
If we can address these things then the vmap_area_lock problem should
just go away - the kernel shouldn't be calling vmalloc/vfree at high
frequency, especially during a compilation workload.
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prev parent reply other threads:[~2014-04-17 23:18 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-10 16:40 Richard Yao
2014-04-10 16:51 ` Andi Kleen
2014-04-10 17:09 ` Richard Yao
2014-04-16 0:28 ` Joonsoo Kim
2014-04-17 23:18 ` Andrew Morton [this message]
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