linux-kernel - Re: [PATCH] mm/numa_balancing: Teach mpol_to

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Message-ID: <87y16po1k3.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Fri, 28 Jun 2024 17:32:12 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
Cc: Matthew Wilcox <willy@...radead.org>,  Tvrtko Ursulin
 <tursulin@...lia.com>,  linux-mm@...ck.org,  linux-kernel@...r.kernel.org,
  kernel-dev@...lia.com,  Mel Gorman <mgorman@...e.de>,  Peter Zijlstra
 <peterz@...radead.org>,  Ingo Molnar <mingo@...hat.com>,  Rik van Riel
 <riel@...riel.com>,  Johannes Weiner <hannes@...xchg.org>,  Dave Hansen
 <dave.hansen@...el.com>,  Andi Kleen <ak@...ux.intel.com>,  Michal Hocko
 <mhocko@...e.com>,  David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] mm/numa_balancing: Teach mpol_to_str about the
 balancing mode

Tvrtko Ursulin <tvrtko.ursulin@...lia.com> writes:

> On 28/06/2024 04:12, Huang, Ying wrote:
>> Hi, Matthew,
>> Matthew Wilcox <willy@...radead.org> writes:
>> 
>>> On Tue, Jun 25, 2024 at 02:26:05PM +0100, Tvrtko Ursulin wrote:
>>>>   		/*
>>>> -		 * Currently, the only defined flags are mutually exclusive
>>>> +		 * The below two flags are mutually exclusive:
>>>>   		 */
>>>>   		if (flags & MPOL_F_STATIC_NODES)
>>>>   			p += snprintf(p, buffer + maxlen - p, "static");
>>>>   		else if (flags & MPOL_F_RELATIVE_NODES)
>>>>   			p += snprintf(p, buffer + maxlen - p, "relative");
>>>> +
>>>> +		if (flags & MPOL_F_NUMA_BALANCING)
>>>> +			p += snprintf(p, buffer + maxlen - p, "balancing");
>>>>   	}
>>>
>>> So if MPOL_F_STATIC_NODES and MPOL_F_NUMA_BALANCING are set, then we
>>> get a string "staticbalancing"?  Is that intended?
>>>
>>> Or are these three all mutually exclusive and that should have been
>>> as "else if"?
>> Yes, this is an issue!
>
> Sigh, my apologies. I was sure I tested it as this patch was part of a
> larger series I have, but then I decided to extract it and send out
> and the problems obviously go deeper. What I think happened is that I
> probably only tested the other direction, setting of via
> mpol_parse_str().
>
> Andrew please dequeue it if you haven't already?
>
>> Dig the git history, in commit 2291990ab36b ("mempolicy: clean-up
>> mpol-to-str() mempolicy formatting"), the support for multiple flags are
>> removed.  I think that we need to restore it.
>> Done some basic testing.  It was found that when
>> MPOL_F_NUMA_BALANCING
>> is set, /proc/PID/numa_maps always display "default".  That is wrong.
>> This make me think that this patch has never been tested!
>> The "default" displaying is introduced in commit 8790c71a18e5
>> ("mm/mempolicy.c: fix mempolicy printing in numa_maps").  We need to fix
>> it firstly for MPOL_F_NUMA_BALANCING with more accurate filtering.  The
>> fix needs to be backported to -stable kernel.
>
> Will you work on this or I can follow up if you want?

Please go forward to work on this, Thanks!

--
Best Regards,
Huang, Ying