From: Andrew Morton <akpm@linux-foundation.org>
To: Shaohua Li <shaohua.li@intel.com>
Cc: linux-mm <linux-mm@kvack.org>,
lkml <linux-kernel@vger.kernel.org>,
Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH]mmap: improve scalability for updating vm_committed_as
Date: Wed, 30 Mar 2011 19:34:04 -0700 [thread overview]
Message-ID: <20110330193404.9525b4e9.akpm@linux-foundation.org> (raw)
In-Reply-To: <1301533003.3981.75.camel@sli10-conroe>
On Thu, 31 Mar 2011 08:56:43 +0800 Shaohua Li <shaohua.li@intel.com> wrote:
> > This is a big change, and it wasn't even changelogged. It's
> > potentially a tremendous increase in the expense of a read from
> > /proc/meminfo, which is a file that lots of tools will be polling.
> > Many of those tools we don't even know about or have access to.
> Assume we don't read /proc/meminfo too often.
That's a poor assumption. top(1) and vmstat(8) read it, for a start.
There will be zillions of locally-developed monitoring tools which read
meminfo.
Now, it could be that something under meminfo reads _already_ does a
massive walk across all CPUs. If so then we'll have already trained
people to avoid reading /proc/meminfo and this change might be
acceptable.
But if this isn't the case then it's quite likely that this change will
hurt some people quite a lot. And, unfortunately, the sort of people
who we will hurt tend to be people who don't run our stuff until a long
time (years) after we wrote it. By which time it's going to be quite
expensive to get a fix down the chain and into their hands.
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next prev parent reply other threads:[~2011-03-31 2:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-30 1:17 [PATCH]mmap: improve scalability for updating vm_committed_as Shaohua Li
2011-03-30 22:51 ` Andrew Morton
2011-03-31 0:56 ` Shaohua Li
2011-03-31 2:34 ` Andrew Morton [this message]
2011-03-31 2:57 ` Shaohua Li
2011-03-31 3:06 ` Andrew Morton
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