[PATCH] mm/memcontrol: update documentation about invoking oom killer

[PATCH] mm/memcontrol: update documentation about invoking oom killer

[Konstantin Khlebnikov]

Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
charge path") memcg invokes oom killer not only for user page-faults.
This means 0-order allocation will either succeed or task get killed.

Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 5361ebec3361..eb47815e137b 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
 
 		Failed allocation in its turn could be returned into
 		userspace as -ENOMEM or silently ignored in cases like
-		disk readahead.  For now OOM in memory cgroup kills
-		tasks iff shortage has happened inside page fault.
+		disk readahead.
+
+		Before 4.19 OOM in memory cgroup killed tasks iff
+		shortage has happened inside page fault, random
+		syscall may fail with ENOMEM or EFAULT. Since 4.19
+		failed memory cgroup allocation invokes oom killer and
+		keeps retrying until it succeeds.
 
 		This event is not raised if the OOM killer is not
 		considered as an option, e.g. for failed high-order

Re: [PATCH] mm/memcontrol: update documentation about invoking oom killer

[Damian Tometzki]

On Sat, 02. Nov 18:16, Konstantin Khlebnikov wrote:
> Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
> charge path") memcg invokes oom killer not only for user page-faults.
> This means 0-order allocation will either succeed or task get killed.
> 
> Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> ---
>  Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 5361ebec3361..eb47815e137b 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
>  
>  		Failed allocation in its turn could be returned into
>  		userspace as -ENOMEM or silently ignored in cases like
> -		disk readahead.  For now OOM in memory cgroup kills
> -		tasks iff shortage has happened inside page fault.
> +		disk readahead.
> +
> +		Before 4.19 OOM in memory cgroup killed tasks iff
Hello Konstantin,

iff --> if :-)

Best regards
Damian


> +		shortage has happened inside page fault, random
> +		syscall may fail with ENOMEM or EFAULT. Since 4.19
> +		failed memory cgroup allocation invokes oom killer and
> +		keeps retrying until it succeeds.
>  
>  		This event is not raised if the OOM killer is not
>  		considered as an option, e.g. for failed high-order
> 

Re: [PATCH] mm/memcontrol: update documentation about invoking oom killer

[Konstantin Khlebnikov]

On 02/11/2019 19.02, Damian Tometzki wrote:
> On Sat, 02. Nov 18:16, Konstantin Khlebnikov wrote:
>> Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
>> charge path") memcg invokes oom killer not only for user page-faults.
>> This means 0-order allocation will either succeed or task get killed.
>>
>> Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>> ---
>>   Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index 5361ebec3361..eb47815e137b 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
>>   
>>   		Failed allocation in its turn could be returned into
>>   		userspace as -ENOMEM or silently ignored in cases like
>> -		disk readahead.  For now OOM in memory cgroup kills
>> -		tasks iff shortage has happened inside page fault.
>> +		disk readahead.
>> +
>> +		Before 4.19 OOM in memory cgroup killed tasks iff
> Hello Konstantin,
> 
> iff --> if :-)
> 

This "iff" is shortened "if and only if".
https://en.wikipedia.org/wiki/If_and_only_if

> Best regards
> Damian
> 
> 
>> +		shortage has happened inside page fault, random
>> +		syscall may fail with ENOMEM or EFAULT. Since 4.19
>> +		failed memory cgroup allocation invokes oom killer and
>> +		keeps retrying until it succeeds.
>>   
>>   		This event is not raised if the OOM killer is not
>>   		considered as an option, e.g. for failed high-order
>>

Re: [PATCH] mm/memcontrol: update documentation about invoking oom killer

[Damian Tometzki]

On Sat, 02. Nov 19:14, Konstantin Khlebnikov wrote:
> 
> 
> On 02/11/2019 19.02, Damian Tometzki wrote:
> > On Sat, 02. Nov 18:16, Konstantin Khlebnikov wrote:
> >> Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
> >> charge path") memcg invokes oom killer not only for user page-faults.
> >> This means 0-order allocation will either succeed or task get killed.
> >>
> >> Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
> >> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> >> ---
> >>   Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
> >>   1 file changed, 7 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> >> index 5361ebec3361..eb47815e137b 100644
> >> --- a/Documentation/admin-guide/cgroup-v2.rst
> >> +++ b/Documentation/admin-guide/cgroup-v2.rst
> >> @@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
> >>   
> >>   		Failed allocation in its turn could be returned into
> >>   		userspace as -ENOMEM or silently ignored in cases like
> >> -		disk readahead.  For now OOM in memory cgroup kills
> >> -		tasks iff shortage has happened inside page fault.
> >> +		disk readahead.
> >> +
> >> +		Before 4.19 OOM in memory cgroup killed tasks iff
> > Hello Konstantin,
> > 
> > iff --> if :-)
> > 
> 
> This "iff" is shortened "if and only if".
> https://en.wikipedia.org/wiki/If_and_only_if

good to know :-)

> 
> > Best regards
> > Damian
> > 
> > 
> >> +		shortage has happened inside page fault, random
> >> +		syscall may fail with ENOMEM or EFAULT. Since 4.19
> >> +		failed memory cgroup allocation invokes oom killer and
> >> +		keeps retrying until it succeeds.
> >>   
> >>   		This event is not raised if the OOM killer is not
> >>   		considered as an option, e.g. for failed high-order
> >>

Re: [PATCH] mm/memcontrol: update documentation about invoking oom killer

[David Rientjes]

On Sat, 2 Nov 2019, Konstantin Khlebnikov wrote:

> Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
> charge path") memcg invokes oom killer not only for user page-faults.
> This means 0-order allocation will either succeed or task get killed.
> 
> Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> ---
>  Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 5361ebec3361..eb47815e137b 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
>  
>  		Failed allocation in its turn could be returned into
>  		userspace as -ENOMEM or silently ignored in cases like
> -		disk readahead.  For now OOM in memory cgroup kills
> -		tasks iff shortage has happened inside page fault.
> +		disk readahead.
> +
> +		Before 4.19 OOM in memory cgroup killed tasks iff
> +		shortage has happened inside page fault, random
> +		syscall may fail with ENOMEM or EFAULT. Since 4.19
> +		failed memory cgroup allocation invokes oom killer and
> +		keeps retrying until it succeeds.
>  
>  		This event is not raised if the OOM killer is not
>  		considered as an option, e.g. for failed high-order

The previous text is obviously incorrect for today's kernels, but I'm 
curious if we should be conflating the documentation here by describing 
the pre-4.19 behavior.  OOM killing no longer happens only on page fault 
so maybe better to document the exact behavior today and not attempt to 
describe differences with previous versions?

Re: [PATCH] mm/memcontrol: update documentation about invoking oom killer

[Konstantin Khlebnikov]

On 03/11/2019 02.55, David Rientjes wrote:
> On Sat, 2 Nov 2019, Konstantin Khlebnikov wrote:
> 
>> Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
>> charge path") memcg invokes oom killer not only for user page-faults.
>> This means 0-order allocation will either succeed or task get killed.
>>
>> Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>> ---
>>   Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index 5361ebec3361..eb47815e137b 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
>>   
>>   		Failed allocation in its turn could be returned into
>>   		userspace as -ENOMEM or silently ignored in cases like
>> -		disk readahead.  For now OOM in memory cgroup kills
>> -		tasks iff shortage has happened inside page fault.
>> +		disk readahead.
>> +
>> +		Before 4.19 OOM in memory cgroup killed tasks iff
>> +		shortage has happened inside page fault, random
>> +		syscall may fail with ENOMEM or EFAULT. Since 4.19
>> +		failed memory cgroup allocation invokes oom killer and
>> +		keeps retrying until it succeeds.
>>   
>>   		This event is not raised if the OOM killer is not
>>   		considered as an option, e.g. for failed high-order
> 
> The previous text is obviously incorrect for today's kernels, but I'm
> curious if we should be conflating the documentation here by describing
> the pre-4.19 behavior.  OOM killing no longer happens only on page fault
> so maybe better to document the exact behavior today and not attempt to
> describe differences with previous versions?
> 

Previous behaviour was here for ages and 4.19 is not so old.
According too https://www.kernel.org/category/releases.html pre-4.19 will
be maintained for couple years at least. Let's keep this tombstone.

I've seen a lot of strange side effects of old behaviour.
Most obscure was a hang inside libc fork() when clone(CLONE_CHILD_SETTID)
silently fails to set child pid =)
https://lore.kernel.org/lkml/20150206162301.18031.32251.stgit@buzz/

Re: [PATCH] mm/memcontrol: update documentation about invoking oom killer

[Michal Hocko]

On Sat 02-11-19 18:16:33, Konstantin Khlebnikov wrote:
> Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
> charge path") memcg invokes oom killer not only for user page-faults.
> This means 0-order allocation will either succeed or task get killed.
> 
> Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")

Is this really appropriate? 8e675f7af507 was correct at the time. It was
29ef680ae7c2 that hasn't updated the documentation. I would just drop
the Fixes tag.

> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> ---
>  Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 5361ebec3361..eb47815e137b 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
>  
>  		Failed allocation in its turn could be returned into
>  		userspace as -ENOMEM or silently ignored in cases like
> -		disk readahead.  For now OOM in memory cgroup kills
> -		tasks iff shortage has happened inside page fault.
> +		disk readahead.
> +
> +		Before 4.19 OOM in memory cgroup killed tasks iff

I would go with Kernels between 3.12 and 4.19 invoked the oom killer
only if shortage has happened inside page fault.

> +		shortage has happened inside page fault, random
> +		syscall may fail with ENOMEM or EFAULT. Since 4.19
> +		failed memory cgroup allocation invokes oom killer and
> +		keeps retrying until it succeeds.
>  
>  		This event is not raised if the OOM killer is not
>  		considered as an option, e.g. for failed high-order

-- 
Michal Hocko
SUSE Labs