RE: [PATCH] mm, oom: normalize the adj to ensure oom_badness return a positive number

[He, Bo]

Sorry, the title is confusing. Change it to: mm, oom: normalize the adj to ensure oom_badness returns a positive number
We are enabling android mobiles. When running stress memory test, there is a bad issue. Some critical processes such as Healthd and watchdogd are killed, while some other processes are still alive.
OOM should kill the tasks whose oom_score are biggest. Many processes use a minus oom_score_adj. oom_badness returns 1 for all of them and their oom_score are all 0.

The patch tries to convert the minus oom_score_adj to a positive number when calculating oom_score. oom_score can keep right process priority sequence.

Without the patch, almost all the processes' oom_score are equal to 0. (cat /proc/XXX/oom_*)
Healthd            -15 0 -941
Servicemanager     -15 0 -941
Vold               -15 0 -941
ia_watchdogd      -15 0 -941
surfaceflinger       -15 0 -941
zygote            -15 0 -941
system_server     -15 0 -941
ndroid.systemui    -11 0 -705

With the patch, we can get different oom_score:
Healthd            -15 59 -941
Servicemanager     -15 89 -941
Vold               -15 60 -941
ia_watchdogd      -15 89 -941
surfaceflinger       -15 145 -941
zygote            -15 122 -941
system_server     -15 166 -941
ndroid.systemui    -11 419 -705


-----Original Message-----
From: David Rientjes [mailto:rientjes@xxxxxxxxxx] 
Sent: Tuesday, March 04, 2014 1:05 PM
To: He, Bo
Cc: linux-kernel@xxxxxxxxxxxxxxx; Ingo Molnar; hannes@xxxxxxxxxxx; oleg@xxxxxxxxxx; kirill.shutemov@xxxxxxxxxxxxxxx; Zhang, Yanmin; yanmin_zhang@xxxxxxxxxxxxxxx; Wang, Biao
Subject: Re: [PATCH] mm, oom: normalize the adj to ensure oom_badness return one

On Mon, 3 Mar 2014, He, Bo wrote:

> if oom_score_adj is a big negative number, such as -941, adj *= 
> totalpages / 1000 will be a big negative number, finally the 
> oom_badness will get 0 points, here normalize the oom_score_adj to 
> ensure oom_badness return the positive number.
> 

Sorry, I have no clue what you're talking about or trying to fix.

A /proc/pid/oom_score_adj of -941 would mean discounting 94.1% of system 
memory from pid's resident memory usage for a system oom condition.  This 
is the effect of adj *= totalpages / 1000 and is working as intended per 
Documentation/filesystems/proc.txt.

oom_badness() will then return the smallest integer possible, 1 (not 0), 
that still allows the process to be killed, that's the effect of 
"return points > 0 ? points : 1".  It never returns 0 as you state, you're 
either not reading the code correctly or not working on any recent kernel.

> Change-Id: I1c56a948ce48b65a1bb63b56ffef07d5d76d7ec8
> Signed-off-by: he, bo <bo.he@xxxxxxxxx>
> Signed-off-by: wang, biao <biao.wang@xxxxxxxxx>
> Reviewed-by: Yanmin Zhang <yanmin_zhang@xxxxxxxxx>
> ---
>  mm/oom_kill.c |    3 +++ 
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 3291e82..5a93986 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -181,6 +181,9 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
>         points -= (points * 3) / 100;
>  
>     /* Normalize to oom_score_adj units */
> +   if(OOM_SCORE_ADJ_MIN < 0)
> +       adj -= OOM_SCORE_ADJ_MIN;
> +
>     adj *= totalpages / 1000;
>     points += adj;
>  
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