Messages in this thread | | | Date | Wed, 30 Mar 2011 19:34:04 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH]mmap: improve scalability for updating vm_committed_as |
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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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