Messages in this thread | | | Date | Thu, 11 Nov 2010 10:30:50 -0800 | From | Mandeep Singh Baines <> | Subject | Re: [PATCH] oom: create a resource limit for oom_adj |
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David Rientjes (rientjes@google.com) wrote: > On Wed, 10 Nov 2010, Mandeep Singh Baines wrote: > > > For ChromiumOS, we'd like to be able to oom_adj a process up/down > > as its leaves/enters the foreground. Currently, it is not possible > > to oom_adj down without CAP_SYS_RESOURCE. This patch creates a new > > resource limit, RLIMIT_OOMADJ, which is works in a similar fashion > > to RLIMIT_NICE. This allows a process's oom_adj to be lowered > > without CAP_SYS_RESOURCE as long as the new value is greater > > than the resource limit. > > > > First of all, oom_adj is deprecated and scheduled for removal in a couple > of years (see Documentation/feature-removal-schedule.txt) so any work in > this area should be targeting oom_score_adj instead. >
Ah. Thanks for the pointer.
> 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.
> having an oom_adj of 0 in the background and +15 in the foreground. If > so, does /proc/sys/vm/oom_kill_allocating_task get you most of what you're > looking for? >
As explained above, oom_kill_allocating_task won't give us what we want.
> I'm wondering if we can avoid yet another resource limit for something > like this. > > > Alternative considered: > > > > * a setuid binary > > * a daemon with CAP_SYS_RESOURCE > > > > Since you don't wan't all processes to be able to reduce their > > oom_adj, a setuid or daemon implementation would be complex. The > > alternatives also have much higher overhead. > > > > 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.
> > Signed-off-by: Mandeep Singh Baines <msb@chromium.org> > > --- > > fs/proc/base.c | 12 ++++++++++-- > > include/asm-generic/resource.h | 5 ++++- > > 2 files changed, 14 insertions(+), 3 deletions(-) > > > > diff --git a/fs/proc/base.c b/fs/proc/base.c > > index f3d02ca..4384013 100644 > > --- a/fs/proc/base.c > > +++ b/fs/proc/base.c > > @@ -462,6 +462,7 @@ static const struct limit_names lnames[RLIM_NLIMITS] = { > > [RLIMIT_NICE] = {"Max nice priority", NULL}, > > [RLIMIT_RTPRIO] = {"Max realtime priority", NULL}, > > [RLIMIT_RTTIME] = {"Max realtime timeout", "us"}, > > + [RLIMIT_OOMADJ] = {"Max OOM adjust", NULL}, > > s/Max/Min, right? >
This is a MAX value because of how resource limits work. On the other hand, it is really controlling the minimum oom_adj. So its a toss up for me. More than happy to change if you prefer Min.
> > }; > > > > /* Display limits for a process */ > > @@ -1057,8 +1058,15 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf, > > } > > > > if (oom_adjust < task->signal->oom_adj && !capable(CAP_SYS_RESOURCE)) { > > - err = -EACCES; > > - goto err_sighand; > > + /* convert oom_adj [15,-17] to rlimit style value [1,33] */ > > + long oom_rlim = OOM_ADJUST_MAX + 1 - oom_adjust; > > + > > Ouch, that's a rather unfortunate mapping. >
Unfortunate but unavoidable. The resource limit code checks to see if the new limit is greater than the limit. This code was based on the can_nice() code in sched.c.
> > + if (oom_rlim > task->signal->rlim[RLIMIT_OOMADJ].rlim_cur) { > > + unlock_task_sighand(task, &flags); > > + put_task_struct(task); > > + err = -EACCES; > > + goto err_sighand; > > err_sighand has duplicate unlock_task_sighand() and put_task_struct(); > since you're missing the task_unlock(task) here, just using goto > err_sighand would suffice. >
D'oh. Forward port error. I should be more careful. Thanks for catching:)
> > + } > > } > > > > if (oom_adjust != task->signal->oom_adj) {
Thank you for reviewing this patch.
Should I send an updated oom_score_adj patch?
Regards, Mandeep
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