[PATCH] mm/oom_kill: fix stale comment in constrained_alloc()

[PATCH] mm/oom_kill: fix stale comment in constrained_alloc()

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

The comment above the __GFP_THISNODE check in constrained_alloc()
is stale and inaccurate: it references __GFP_NOFAIL (which is not
checked here), claims the OOM killer does "random task kill" (it
uses badness scores), and mentions CONSTRAINT_THISNODE (which was
never added to the enum).  Replace it with a description that
matches the actual code behavior.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 mm/oom_kill.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5f372f6e26fa..4b5c70aaece4 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -268,9 +268,9 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 	if (!oc->zonelist)
 		return CONSTRAINT_NONE;
 	/*
-	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
-	 * to kill current.We have to random task kill in this case.
-	 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
+	 * __GFP_THISNODE means the allocation is restricted to a single node.
+	 * There is no dedicated constraint type for this case, so return
+	 * CONSTRAINT_NONE and let the normal OOM handling proceed.
 	 */
 	if (oc->gfp_mask & __GFP_THISNODE)
 		return CONSTRAINT_NONE;
-- 
2.25.1

Re: [PATCH] mm/oom_kill: fix stale comment in constrained_alloc()

[Michal Hocko]

On Thu 13-08-26 11:06:54, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> The comment above the __GFP_THISNODE check in constrained_alloc()
> is stale and inaccurate: it references __GFP_NOFAIL (which is not
> checked here), claims the OOM killer does "random task kill" (it
> uses badness scores), and mentions CONSTRAINT_THISNODE (which was
> never added to the enum).  Replace it with a description that
> matches the actual code behavior.

The comment is indeed confusing and stale. Your update unfortunatelly as
well. This code is simply unreachable because we never trigger global
OOM with __GFP_THISNODE (see __alloc_pages_may_oom) and for memcg OOM
__GFP_THISNODE is immaterial.

> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> ---
>  mm/oom_kill.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5f372f6e26fa..4b5c70aaece4 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -268,9 +268,9 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
>  	if (!oc->zonelist)
>  		return CONSTRAINT_NONE;
>  	/*
> -	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
> -	 * to kill current.We have to random task kill in this case.
> -	 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
> +	 * __GFP_THISNODE means the allocation is restricted to a single node.
> +	 * There is no dedicated constraint type for this case, so return
> +	 * CONSTRAINT_NONE and let the normal OOM handling proceed.
>  	 */
>  	if (oc->gfp_mask & __GFP_THISNODE)
>  		return CONSTRAINT_NONE;
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm/oom_kill: fix stale comment in constrained_alloc()

[Ye Liu]

在 2026/8/13 16:43, Michal Hocko 写道:
> On Thu 13-08-26 11:06:54, Ye Liu wrote:
>> From: Ye Liu <liuye@kylinos.cn>
>>
>> The comment above the __GFP_THISNODE check in constrained_alloc()
>> is stale and inaccurate: it references __GFP_NOFAIL (which is not
>> checked here), claims the OOM killer does "random task kill" (it
>> uses badness scores), and mentions CONSTRAINT_THISNODE (which was
>> never added to the enum).  Replace it with a description that
>> matches the actual code behavior.
> 
> The comment is indeed confusing and stale. Your update unfortunatelly as
> well. This code is simply unreachable because we never trigger global
> OOM with __GFP_THISNODE (see __alloc_pages_may_oom) and for memcg OOM
> __GFP_THISNODE is immaterial.
> 
I directly deleted the invalid code and sent v2.
>> Signed-off-by: Ye Liu <liuye@kylinos.cn>
>> ---
>>  mm/oom_kill.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
>> index 5f372f6e26fa..4b5c70aaece4 100644
>> --- a/mm/oom_kill.c
>> +++ b/mm/oom_kill.c
>> @@ -268,9 +268,9 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
>>  	if (!oc->zonelist)
>>  		return CONSTRAINT_NONE;
>>  	/*
>> -	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
>> -	 * to kill current.We have to random task kill in this case.
>> -	 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
>> +	 * __GFP_THISNODE means the allocation is restricted to a single node.
>> +	 * There is no dedicated constraint type for this case, so return
>> +	 * CONSTRAINT_NONE and let the normal OOM handling proceed.
>>  	 */
>>  	if (oc->gfp_mask & __GFP_THISNODE)
>>  		return CONSTRAINT_NONE;
>> -- 
>> 2.25.1
> 

-- 
Thanks,
Ye Liu