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SubjectRe: [PATCH] oom: create a resource limit for oom_adj
David Rientjes (rientjes@google.com) wrote:
> On Thu, 11 Nov 2010, Mandeep Singh Baines wrote:
>
> > > What is the anticipated use case for this? We know that you want to lower
> > > oom_adj without CAP_SYS_RESOURCE, but what's the expected behavior when an
> > > app moves from foreground to background? I assume it's something like
> >
> > The focus here is the web browser's tabs. In our case, each is a process. If
> > OOM is going to kill a process, you'd rather it kill the tab you looked at
> > hours ago instead of the one you're looking at now. So you'd like to have a
> > policy where the LRU tab gets killed first. We'd like to use oom_score_adj
> > as the mechanism to implement an LRU policy like this.
> >
>
> Hmm, at first glance that seems potentially dangerous if the current tab
> generates a burt of memory allocations and it ends up killing all other
> tabs before finally targeting the culprit whereas currently the heuristic
> should do a good job of finding this problematic tab and killing it
> instantly.
>

If you're watching a movie, video chatting, playing a game, etc. What
would you rather have killed: the current tab you are interacting with or
some tab you opened a while back and are no longer interacting with.

> Perhaps that can't happen and it probably doesn't even matter:
> oom_score_adj allows users to determine which process to kill regardless
> of the underlying reason.
>
> > > What do you anticipate will be writing to oom_score_adj with this patch,
> > > the app itself?
> >
> > A process in the browser session will do the adusting. We'd rather not give
> > it CAP_SYS_RESOURCE. It should only be allowed to change oom_score_adj up
> > and down within the bounds set by the administrator. Analagous to renice()
> > which we also do using a similar policy.
> >
>
> So as more and more tabs get used, the least recently used tab gets its
> oom_score_adj raised higher and higher until it is reused itself and then
> it gets reset back to 0 for the current tab?
>

Exactly.

> Is there a reason you don't want to give the underlying browser session
> process CAP_SYS_RESOURCE? Will it not be enforcing resource limits to

Security. We want to use the least-privilege possible. We really want to
avoid giving special privileges to the browser. You shouldn't need
administrative privileges to run the browser. We'd like for oom_score_adj
to work the same as nice. An unprivileged user can nice up and down as
long as the new setting is within the administratively configured
resource limit: ulimit -e.

> ensure tabs don't deplete all memory when certain sites are opened? Are
> you concerned that it may deplete all memory itself (for which case you
> could raise its own oom_score_adj, which is a proportion of available
> memory so you can define where that point of depletiong is)?


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