Re: RSS accounting (was: Re: 2.6.19-rc1-mm1)

On Wed, 2006-10-11 at 06:07 -0600, Eric W. Biederman wrote:
Arjan van de Ven <arjan@xxxxxxxxxxxxx> writes:

On Tue, 2006-10-10 at 17:54 -0600, Eric W. Biederman wrote:

For processes shared pages are not special.

Actually the above is not quite true you can map a shared page twice
into the same process but in practice it rarely happens.

yeah I'm entirely fine with ignoring that case (or making the person who
does it pay for it :)


depends on what question you want to answer with RSS.
If the question is "workload working set size" then you are right. If
the question is "how much ram does my application cause to be used" the
answer is FAR less clear....

There are two basic concerns. How do you keep an application from
going crazy and trashing the rest of your system? A question on what
number do you need to implement a resource limit.

yet at the same time if 2 apps mmap a shared file, and app 1 keeps it in
pagecache, it doesn't cause app2 to trash, or rather, it's not like if
app 2 did NOT have the page from that file, the system wouldn't trash.


You seem to have an implicit definition on what RSS should mean; but
it's implicit. Mind making an explicit definition of what RSS should be
in your opinion? I think that's the biggest problem we have right now;
several people have different ideas about what it should/could be, and
as such we're not talking about the same thing. Lets first agree/specify
what it SHOULD mean, and then we can figure out what gets counted for
that ;)

Well I tried to defined it in terms of what you can use it for.

I would define the resident set size as the total number of bytes
of physical RAM that a process (or set of processes) is using,
irrespective of the rest of the system.


So I think the counting should be primarily about what is mapped into
the page tables. But other things can be added as is appropriate or
easy.

The practical effect should be that an application that needs more
pages than it's specified RSS to avoid thrashing should thrash but
it shouldn't take the rest of the system with it.


so by your definition, hugepages are part of RSS.

Ken: what is your definition of RSS ?


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