linux-kernel - Re: [PATCH 3/3] staging: lowmemorykiller: select the task with maximum rss to kill

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Message-ID: <alpine.DEB.2.10.1606211313210.28466@chino.kir.corp.google.com>
Date:	Tue, 21 Jun 2016 13:14:36 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
cc:	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, arve@...roid.com, riandrews@...roid.com
Subject: Re: [PATCH 3/3] staging: lowmemorykiller: select the task with
 maximum rss to kill

On Tue, 21 Jun 2016, Ganesh Mahendran wrote:

> Current task selecting logic in LMK does not fully aware of the memory
> pressure. It may select the task with maximum score adj, but with
> least tasksize.
> 
> For example, if min_score_adj is 200, and there are 2 tasks in system:
>    task a: score adj 500, tasksize 200M
>    task b: score adj 1000, tasksize 1M
> Current LMK logic will select *task b*. But now the system already have
> much memory pressure.
> 
> We should select the task with maximum task from all the tasks which
> score adj >= min_score_adj.
> 

Unfortunately, I'm not sure that we can get away with this although I 
agree that it is a better result (kill a large process, avoid lowmem or 
oom for longer).

It changes the kill order for systems that have already fine-tuned their 
oom_score_adj settings and can regress because of this change.  If systems 
really want task b to be killed above, this breaks and they have no 
immediate way of fixing it.