linux-kernel - Re: [bug report] resctrl high memory comsumption

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Date:   Wed, 8 Jan 2020 13:54:39 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>, Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org
Subject: Re: [bug report] resctrl high memory comsumption

Hi Fenghua,

On 1/8/2020 1:42 PM, Fenghua Yu wrote:
> On Wed, Jan 08, 2020 at 12:42:17PM -0800, Reinette Chatre wrote:
>> Hi Fenghua,
>> On 1/8/2020 12:23 PM, Fenghua Yu wrote:
>>> On Wed, Jan 08, 2020 at 09:07:41AM -0800, Shakeel Butt wrote:
>>>> Recently we had a bug in the system software writing the same pids to
>>>> the tasks file of resctrl group multiple times. The resctrl code
>>> Subject: [RFC PATCH] x86/resctrl: Fix redundant task movements
>> I think your fix would address this specific use case but a slightly
>> different use case will still encounter the problem of high memory
>> consumption. If for example, sleeping tasks are moved (many times)
>> between resource or monitoring groups then their task_works queue would
>> just keep growing. It seems that a call to task_work_cancel() before
>> adding a new work item should address all these cases?
> 
> The checking code in this patch is also helpful to avoid redundant
> task move preparation (kzalloc(), task_work_add(), etc) in the same
> rdtgroup.

Indeed.

> 
> How about adding both the checking code and task_work_cancel()?

That does sound good to me.

There is something in the current implementation that I would appreciate
your feedback on: Currently the task's closid and rmid are initialized
_after_ the call to task_work_add() succeeds. Should these not be
initialized before the call to task_work_add()?

Thank you

Reinette