[PATCH] oom: create a resource limit for oom_adj

[PATCH] oom: create a resource limit for oom_adj

[Mandeep Singh Baines]

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.

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.

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},
 };
 
 /* 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;
+
+		if (oom_rlim > task->signal->rlim[RLIMIT_OOMADJ].rlim_cur) {
+			unlock_task_sighand(task, &flags);
+			put_task_struct(task);
+			err = -EACCES;
+			goto err_sighand;
+		}
 	}
 
 	if (oom_adjust != task->signal->oom_adj) {
diff --git a/include/asm-generic/resource.h b/include/asm-generic/resource.h
index 587566f..a8640a4 100644
--- a/include/asm-generic/resource.h
+++ b/include/asm-generic/resource.h
@@ -45,7 +45,9 @@
 					   0-39 for nice level 19 .. -20 */
 #define RLIMIT_RTPRIO		14	/* maximum realtime priority */
 #define RLIMIT_RTTIME		15	/* timeout for RT tasks in us */
-#define RLIM_NLIMITS		16
+#define RLIMIT_OOMADJ		16	/* max oom_adj allowed to lower to
+					   0-32 for oom level 15 .. -17 */
+#define RLIM_NLIMITS		17
 
 /*
  * SuS says limits have to be unsigned.
@@ -86,6 +88,7 @@
 	[RLIMIT_MSGQUEUE]	= {   MQ_BYTES_MAX,   MQ_BYTES_MAX },	\
 	[RLIMIT_NICE]		= { 0, 0 },				\
 	[RLIMIT_RTPRIO]		= { 0, 0 },				\
+	[RLIMIT_OOMADJ]		= { 0, 0 },				\
 	[RLIMIT_RTTIME]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
 }
 
-- 
1.7.3.1

Re: [PATCH] oom: create a resource limit for oom_adj

[David Rientjes]

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.

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 
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?

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?

> 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?

>  };
>  
>  /* 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.

> +		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.

> +		}
>  	}
>  
>  	if (oom_adjust != task->signal->oom_adj) {

Re: [PATCH] oom: create a resource limit for oom_adj

[Mandeep Singh Baines]

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

Re: [PATCH] oom: create a resource limit for oom_adj

[David Rientjes]

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.

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?

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 
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)?

Re: [PATCH] oom: create a resource limit for oom_adj

[Mandeep Singh Baines]

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)?

Re: [PATCH] oom: create a resource limit for oom_adj

[David Rientjes]

On Thu, 11 Nov 2010, Mandeep Singh Baines wrote:

> > 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.
> 

Well, it's a tangential point, but I'd personally prefer that my existing 
tabs that I've decided to leave open are guaranteed to remain open 
regardless of where I'm browsing next (they could hold valuable data that 
I can't easily get back) and avoid having all of them sacrificed out from 
under me for the newly opened tab.  I can always go back and close those 
tabs for more memory if I know I don't need them anymore and then retry 
the failed allocation.

> > 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.
> 

We don't necessarily want arbitrary tasks to be able to decrease their 
oom_score_adj back to 0 if a CAP_SYS_RESOURCE thread has elevated it, 
that's part of the reason for the restriction (in addition to decreasing 
your own oom_score_adj all the way to OOM_SCORE_ADJ_MIN).

Would it suffice to allow a task to decrease its oom_score_adj back to the 
highest value that a CAP_SYS_RESOURCE thread set it or its inherited value 
at fork?  Assuming the thread that has forked it has oom_score_adj of 0, 
each tab could decrease it back from 0 upon activation unless a 
CAP_SYS_RESOURCE thread elevated it to something higher.

To do this, we'd need to save the highest oom_score_adj set by a 
CAP_SYS_RESOURCE in struct signal_struct.

Re: [PATCH] oom: create a resource limit for oom_adj

[Mandeep Singh Baines]

David Rientjes (rientjes@google.com) wrote:
> On Thu, 11 Nov 2010, Mandeep Singh Baines wrote:
> 
> > > 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.
> > 
> 
> Well, it's a tangential point, but I'd personally prefer that my existing 
> tabs that I've decided to leave open are guaranteed to remain open 
> regardless of where I'm browsing next (they could hold valuable data that 
> I can't easily get back) and avoid having all of them sacrificed out from 
> under me for the newly opened tab.  I can always go back and close those 
> tabs for more memory if I know I don't need them anymore and then retry 
> the failed allocation.
> 
> > > 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.
> > 
> 
> We don't necessarily want arbitrary tasks to be able to decrease their 
> oom_score_adj back to 0 if a CAP_SYS_RESOURCE thread has elevated it, 
> that's part of the reason for the restriction (in addition to decreasing 
> your own oom_score_adj all the way to OOM_SCORE_ADJ_MIN).
> 
> Would it suffice to allow a task to decrease its oom_score_adj back to the 
> highest value that a CAP_SYS_RESOURCE thread set it or its inherited value 
> at fork?  Assuming the thread that has forked it has oom_score_adj of 0, 
> each tab could decrease it back from 0 upon activation unless a 
> CAP_SYS_RESOURCE thread elevated it to something higher.
> 
> To do this, we'd need to save the highest oom_score_adj set by a 
> CAP_SYS_RESOURCE in struct signal_struct.

Sounds good to me. I'll start working on this patch.

Thanks,
Mandeep

[PATCH] oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down

[Mandeep Singh Baines]

We'd like to be able to oom_score_adj a process up/down as its
enters/leaves the foreground. Currently, it is not possible to oom_adj
down without CAP_SYS_RESOURCE. This patch allows a task to decrease
its oom_score_adj back to the value that a CAP_SYS_RESOURCE thread set
it or its inherited value at fork. Assuming the thread that has forked
it has oom_score_adj of 0, each tab could decrease it back from 0 upon
activation unless a CAP_SYS_RESOURCE thread elevated it to something
higher.

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.

This patch updated based on feedback from
David Rientjes <rientjes@google.com>.

Change-Id: If8f52363fd6c156e1730f43148aee987260e9c72
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
---
 fs/proc/base.c        |    4 +++-
 include/linux/sched.h |    2 ++
 2 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index f3d02ca..e617413 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1164,7 +1164,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 		goto err_task_lock;
 	}
 
-	if (oom_score_adj < task->signal->oom_score_adj &&
+	if (oom_score_adj < task->signal->oom_score_adj_min &&
 			!capable(CAP_SYS_RESOURCE)) {
 		err = -EACCES;
 		goto err_sighand;
@@ -1177,6 +1177,8 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 			atomic_dec(&task->mm->oom_disable_count);
 	}
 	task->signal->oom_score_adj = oom_score_adj;
+	if (capable(CAP_SYS_RESOURCE))
+		task->signal->oom_score_adj_min = oom_score_adj;
 	/*
 	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
 	 * always attainable.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f53cdf2..2a71ee0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -626,6 +626,8 @@ struct signal_struct {
 
 	int oom_adj;		/* OOM kill score adjustment (bit shift) */
 	int oom_score_adj;	/* OOM kill score adjustment */
+	int oom_score_adj_min;	/* OOM kill score adjustment minimum value.
+				 * Only settable by CAP_SYS_RESOURCE. */
 
 	struct mutex cred_guard_mutex;	/* guard against foreign influences on
 					 * credential calculations
-- 
1.7.3.1

Re: [PATCH] oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down

[David Rientjes]

On Fri, 12 Nov 2010, Mandeep Singh Baines wrote:

> We'd like to be able to oom_score_adj a process up/down as its
> enters/leaves the foreground. Currently, it is not possible to oom_adj
> down without CAP_SYS_RESOURCE. This patch allows a task to decrease
> its oom_score_adj back to the value that a CAP_SYS_RESOURCE thread set
> it or its inherited value at fork. Assuming the thread that has forked
> it has oom_score_adj of 0, each tab could decrease it back from 0 upon
> activation unless a CAP_SYS_RESOURCE thread elevated it to something
> higher.
> 

oom_score_adj_min doesn't appear to be inherited at fork in your patch.

> 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.
> 

This behavior should be documented in Documentation/filesystems/proc.txt.

> This patch updated based on feedback from
> David Rientjes <rientjes@google.com>.
> 
> Change-Id: If8f52363fd6c156e1730f43148aee987260e9c72

I know what a Change-Id is , but nobody else here does :)

> Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
> ---
>  fs/proc/base.c        |    4 +++-
>  include/linux/sched.h |    2 ++
>  2 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index f3d02ca..e617413 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1164,7 +1164,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
>  		goto err_task_lock;
>  	}
>  
> -	if (oom_score_adj < task->signal->oom_score_adj &&
> +	if (oom_score_adj < task->signal->oom_score_adj_min &&
>  			!capable(CAP_SYS_RESOURCE)) {
>  		err = -EACCES;
>  		goto err_sighand;
> @@ -1177,6 +1177,8 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
>  			atomic_dec(&task->mm->oom_disable_count);
>  	}
>  	task->signal->oom_score_adj = oom_score_adj;
> +	if (capable(CAP_SYS_RESOURCE))
> +		task->signal->oom_score_adj_min = oom_score_adj;
>  	/*
>  	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
>  	 * always attainable.
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f53cdf2..2a71ee0 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -626,6 +626,8 @@ struct signal_struct {
>  
>  	int oom_adj;		/* OOM kill score adjustment (bit shift) */
>  	int oom_score_adj;	/* OOM kill score adjustment */
> +	int oom_score_adj_min;	/* OOM kill score adjustment minimum value.
> +				 * Only settable by CAP_SYS_RESOURCE. */
>  
>  	struct mutex cred_guard_mutex;	/* guard against foreign influences on
>  					 * credential calculations

[PATCH v2] oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down

[Mandeep Singh Baines]

Hi,

Attached is V2 of this patch. Since V1:

* Added documentation in Documentation/filesystems/proc.txt
* Copy oom_score_adj_min value across a fork

An alternative to this patch would be to expose oom_score_adj_min via
proc (suggested by Kosaki Motohiro). You could allow non-CAP_SYS_RESOURCE
processes to irreversibly increase the minimum. That would give you
similar semantics to a resource limit and would give you a bit more
control but it means adding another proc variable.

Regards,
Mandeep

---

We'd like to be able to oom_score_adj a process up/down as its
enters/leaves the foreground. Currently, it is not possible to oom_adj
down without CAP_SYS_RESOURCE. This patch allows a task to decrease
its oom_score_adj back to the value that a CAP_SYS_RESOURCE thread set
it or its inherited value at fork. Assuming the thread that has forked
it has oom_score_adj of 0, each tab process could decrease it back from
0 upon activation unless a CAP_SYS_RESOURCE thread elevated it to
something higher.

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.

This patch updated from original patch based on feedback from
David Rientjes <rientjes@google.com>.

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
---
 Documentation/filesystems/proc.txt |    4 ++++
 fs/proc/base.c                     |    4 +++-
 include/linux/sched.h              |    2 ++
 kernel/fork.c                      |    1 +
 4 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index e73df27..7139c50 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1296,6 +1296,10 @@ scaled linearly with /proc/<pid>/oom_score_adj.
 Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
 other with its scaled value.
 
+The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
+value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
+requires CAP_SYS_RESOURCE.
+
 NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see
 Documentation/feature-removal-schedule.txt.
 
diff --git a/fs/proc/base.c b/fs/proc/base.c
index f3d02ca..e617413 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1164,7 +1164,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 		goto err_task_lock;
 	}
 
-	if (oom_score_adj < task->signal->oom_score_adj &&
+	if (oom_score_adj < task->signal->oom_score_adj_min &&
 			!capable(CAP_SYS_RESOURCE)) {
 		err = -EACCES;
 		goto err_sighand;
@@ -1177,6 +1177,8 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 			atomic_dec(&task->mm->oom_disable_count);
 	}
 	task->signal->oom_score_adj = oom_score_adj;
+	if (capable(CAP_SYS_RESOURCE))
+		task->signal->oom_score_adj_min = oom_score_adj;
 	/*
 	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
 	 * always attainable.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f53cdf2..2a71ee0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -626,6 +626,8 @@ struct signal_struct {
 
 	int oom_adj;		/* OOM kill score adjustment (bit shift) */
 	int oom_score_adj;	/* OOM kill score adjustment */
+	int oom_score_adj_min;	/* OOM kill score adjustment minimum value.
+				 * Only settable by CAP_SYS_RESOURCE. */
 
 	struct mutex cred_guard_mutex;	/* guard against foreign influences on
 					 * credential calculations
diff --git a/kernel/fork.c b/kernel/fork.c
index 3b159c5..0979527 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -907,6 +907,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 
 	sig->oom_adj = current->signal->oom_adj;
 	sig->oom_score_adj = current->signal->oom_score_adj;
+	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
 
 	mutex_init(&sig->cred_guard_mutex);
 
-- 
1.7.3.1

Re: [PATCH v2] oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down

[David Rientjes]

On Mon, 15 Nov 2010, Mandeep Singh Baines wrote:

> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index f3d02ca..e617413 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1164,7 +1164,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
>  		goto err_task_lock;
>  	}
>  
> -	if (oom_score_adj < task->signal->oom_score_adj &&
> +	if (oom_score_adj < task->signal->oom_score_adj_min &&
>  			!capable(CAP_SYS_RESOURCE)) {
>  		err = -EACCES;
>  		goto err_sighand;
> @@ -1177,6 +1177,8 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
>  			atomic_dec(&task->mm->oom_disable_count);
>  	}
>  	task->signal->oom_score_adj = oom_score_adj;
> +	if (capable(CAP_SYS_RESOURCE))
> +		task->signal->oom_score_adj_min = oom_score_adj;
>  	/*
>  	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
>  	 * always attainable.

This should be has_capability_noaudit(current, CAP_SYS_RESOURCE) instead, 
we don't want an audit message to be emitted when checking if 
oom_score_adj_min should be set.

Other than that:

Acked-by: David Rientjes <rientjes@google.com>

[PATCH v3] oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down

[Mandeep Singh Baines]

We'd like to be able to oom_score_adj a process up/down as its
enters/leaves the foreground. Currently, it is not possible to oom_adj
down without CAP_SYS_RESOURCE. This patch allows a task to decrease
its oom_score_adj back to the value that a CAP_SYS_RESOURCE thread set
it or its inherited value at fork. Assuming the thread that has forked
it has oom_score_adj of 0, each tab process could decrease it back from
0 upon activation unless a CAP_SYS_RESOURCE thread elevated it to
something higher.

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.

This patch updated from original patch based on feedback from
David Rientjes <rientjes@google.com>.

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Acked-by: David Rientjes <rientjes@google.com>
---
 Documentation/filesystems/proc.txt |    4 ++++
 fs/proc/base.c                     |    4 +++-
 include/linux/sched.h              |    2 ++
 kernel/fork.c                      |    1 +
 4 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index e73df27..7139c50 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1296,6 +1296,10 @@ scaled linearly with /proc/<pid>/oom_score_adj.
 Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
 other with its scaled value.
 
+The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
+value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
+requires CAP_SYS_RESOURCE.
+
 NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see
 Documentation/feature-removal-schedule.txt.
 
diff --git a/fs/proc/base.c b/fs/proc/base.c
index f3d02ca..7b1a9df 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1164,7 +1164,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 		goto err_task_lock;
 	}
 
-	if (oom_score_adj < task->signal->oom_score_adj &&
+	if (oom_score_adj < task->signal->oom_score_adj_min &&
 			!capable(CAP_SYS_RESOURCE)) {
 		err = -EACCES;
 		goto err_sighand;
@@ -1177,6 +1177,8 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 			atomic_dec(&task->mm->oom_disable_count);
 	}
 	task->signal->oom_score_adj = oom_score_adj;
+	if (has_capability_noaudit(current, CAP_SYS_RESOURCE))
+		task->signal->oom_score_adj_min = oom_score_adj;
 	/*
 	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
 	 * always attainable.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f53cdf2..2a71ee0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -626,6 +626,8 @@ struct signal_struct {
 
 	int oom_adj;		/* OOM kill score adjustment (bit shift) */
 	int oom_score_adj;	/* OOM kill score adjustment */
+	int oom_score_adj_min;	/* OOM kill score adjustment minimum value.
+				 * Only settable by CAP_SYS_RESOURCE. */
 
 	struct mutex cred_guard_mutex;	/* guard against foreign influences on
 					 * credential calculations
diff --git a/kernel/fork.c b/kernel/fork.c
index 3b159c5..0979527 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -907,6 +907,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 
 	sig->oom_adj = current->signal->oom_adj;
 	sig->oom_score_adj = current->signal->oom_score_adj;
+	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
 
 	mutex_init(&sig->cred_guard_mutex);
 
-- 
1.7.3.1

Re: [PATCH] oom: create a resource limit for oom_adj

[KOSAKI Motohiro]

Hi Mandeep,

> 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.
> 
> 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.
> 
> 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(-)

This concept sound useful for embedeed. but I dislike this interface
a bit. Why don't you create /proc/{pid}/oom_adj_lower_bound or similar? 
It is more straight forward because oom_adj are already using /proc.

I also think 15..-17 to 0-32 convertion is a bit user unfriendly.


> 
> 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},
>  };
>  
>  /* 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;
> +
> +		if (oom_rlim > task->signal->rlim[RLIMIT_OOMADJ].rlim_cur) {

two points.

1) task->signal->rlim[RLIMIT_OOMADJ].rlim_cur is incorrect.
   please use task_rlimit().

2) If process has CAP_SYS_RESOURCE, we should ignore RLIMIT_OOMADJ for
   backword compatibility. CAP_NICE do so. (see below)

------------------------------------------------------------------
int can_nice(const struct task_struct *p, const int nice)
{
        /* convert nice value [19,-20] to rlimit style value [1,40] */
        int nice_rlim = 20 - nice;

        return (nice_rlim <= task_rlimit(p, RLIMIT_NICE) ||
                capable(CAP_SYS_NICE));
}
------------------------------------------------------------------



> +			unlock_task_sighand(task, &flags);
> +			put_task_struct(task);
> +			err = -EACCES;
> +			goto err_sighand;
> +		}
>  	}
>  
>  	if (oom_adjust != task->signal->oom_adj) {
> diff --git a/include/asm-generic/resource.h b/include/asm-generic/resource.h
> index 587566f..a8640a4 100644
> --- a/include/asm-generic/resource.h
> +++ b/include/asm-generic/resource.h
> @@ -45,7 +45,9 @@
>  					   0-39 for nice level 19 .. -20 */
>  #define RLIMIT_RTPRIO		14	/* maximum realtime priority */
>  #define RLIMIT_RTTIME		15	/* timeout for RT tasks in us */
> -#define RLIM_NLIMITS		16
> +#define RLIMIT_OOMADJ		16	/* max oom_adj allowed to lower to
> +					   0-32 for oom level 15 .. -17 */
> +#define RLIM_NLIMITS		17
>  
>  /*
>   * SuS says limits have to be unsigned.
> @@ -86,6 +88,7 @@
>  	[RLIMIT_MSGQUEUE]	= {   MQ_BYTES_MAX,   MQ_BYTES_MAX },	\
>  	[RLIMIT_NICE]		= { 0, 0 },				\
>  	[RLIMIT_RTPRIO]		= { 0, 0 },				\
> +	[RLIMIT_OOMADJ]		= { 0, 0 },				\

I don't think 0 is good initial value because 0 mean oom_adj==15.



>  	[RLIMIT_RTTIME]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
>  }
>  
> -- 
> 1.7.3.1
> 

Re: [PATCH] oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down

[Bodo Eggert]

Mandeep Singh Baines <msb@google.com> wrote:

> We'd like to be able to oom_score_adj a process up/down as its
> enters/leaves the foreground. Currently, it is not possible to oom_adj
> down without CAP_SYS_RESOURCE. This patch allows a task to decrease
> its oom_score_adj back to the value that a CAP_SYS_RESOURCE thread set
> it or its inherited value at fork. Assuming the thread that has forked
> it has oom_score_adj of 0, each tab

process

> could decrease it back from 0 upon 
> activation unless a CAP_SYS_RESOURCE thread elevated it to something
> higher.