Message-ID: <47ED354C.2040502@linux.vnet.ibm.com>
Date:	Fri, 28 Mar 2008 23:43:32 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Paul Menage <menage@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelianov <xemul@...nvz.org>,
	Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][0/3] Virtual address space control for cgroups (v2)

Paul Menage wrote:
> On Thu, Mar 27, 2008 at 8:59 PM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>>  > Java (or at least, Sun's JRE) is an example of a common application
>>  > that does this. It creates a huge heap mapping at startup, and faults
>>  > it in as necessary.
>>  >
>>
>>  Isn't this controlled by the java -Xm options?
>>
> 
> Probably - that was just an example, and the behaviour of Java isn't
> exactly unreasonable. A different example would be an app that maps a
> massive database file, but only pages small amounts of it in at any
> one time.
> 
>>  I understand, but
>>
>>  1. The system by default enforces overcommit on most distros, so why should we
>>  not have something similar and that flexible for cgroups.
> 
> Right, I guess I should make it clear that I'm *not* arguing that we
> shouldn't have a virtual address space limit subsystem.
> 
> My main arguments in this and my previous email were to back up my
> assertion that there are a significant set of real-world cases where
> it doesn't help, and hence it should be a separate subsystem that can
> be turned on or off as desired.
> 
> It strikes me that when split into its own subsystem, this is going to
> be very simple - basically just a resource counter and some file
> handlers. We should probably have something like
> include/linux/rescounter_subsys_template.h, so you can do:
> 
> #define SUBSYS_NAME va
> #define SUBSYS_UNIT_SUFFIX in_bytes
> #include <linux/rescounter_subsys_template.h>
> 
> then all you have to add are the hooks to call the rescounter
> charge/uncharge functions and you're done. It would be nice to have a
> separate trivial subsystem like this for each of the rlimit types, not
> just virtual address space.
> 

OK, I'll consider doing a separate controller, once we get the mm->owner issue
sorted out.

>>   And specifying
>>  > them manually requires either unusually clueful users (most of whom
>>  > have enough trouble figuring out how much physical memory they'll
>>  > need, and would just set very high virtual address space limits) or
>>  > sysadmins with way too much time on their hands ...
>>  >
>>
>>  It's a one time thing to setup for sysadmins
>>
> 
> Sure, it's a one-time thing to setup *if* your cluster workload is
> completely static.
> 
>>  > As I said, I think focussing on ways to tell apps that they're running
>>  > low on physical memory would be much more productive.
>>  >
>>
>>  We intend to do that as well. We intend to have user space OOM notification.
> 
> We've been playing with a user-space OOM notification system at Google
> - it's on my TODO list to push it to mainline (as an independent
> subsystem, since either cpusets or the memory controller can be used
> to cause OOMs that are localized to a cgroup). What we have works
> pretty well but I think our interface is a bit too much of a kludge at
> this point.

It's good to know you have something generic working. I was planning to start
work on it later.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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