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

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Date: Wed, 26 Jun 2024 12:51:08 +0100
From: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
To: "Huang, Ying" <ying.huang@...el.com>, Tvrtko Ursulin <tursulin@...lia.com>
Cc: 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>,
 "Matthew Wilcox (Oracle)" <willy@...radead.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


On 26/06/2024 09:48, Huang, Ying wrote:
> Tvrtko Ursulin <tursulin@...lia.com> writes:
> 
>> From: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
>>
>> If a task has had MPOL_F_NUMA_BALANCING set it is useful to show that in
> 
> IIUC, MPOL_F_NUMA_BALANCING works for VMA area via mbind() too.

Ah okay.. I think I forgot to actually check and went by what commit 
text of bda420b98505 said, which is probably outdated.

>> procfs. Teach the mpol_to_str helper about its existance and while at it
>> update the comment to account for "weighted interleave" when suggesting
>> a recommended buffer size.
> 
> Otherwise LGTM, Thanks!
> 
> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

Thank you! Would you have an idea of which tree this should go to aka 
which maintainer to ask to merge it?

Second question - I also have a patch which enables choosing balancing 
for tmpfs (mpol_parse_str) but I am unsure of its value. It would make 
things symmetrical, but is there some other benefit I don't know. Any 
thoughts on this?

Regards,

Tvrtko

>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
>> References: bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes")
>> Cc: Huang Ying <ying.huang@...el.com>
>> Cc: Mel Gorman <mgorman@...e.de>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Rik van Riel <riel@...riel.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
>> Cc: Dave Hansen <dave.hansen@...el.com>
>> Cc: Andi Kleen <ak@...ux.intel.com>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: David Rientjes <rientjes@...gle.com>
>> ---
>>   mm/mempolicy.c | 10 +++++++---
>>   1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index aec756ae5637..d147287c4505 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -3293,8 +3293,9 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
>>    * @pol:  pointer to mempolicy to be formatted
>>    *
>>    * Convert @pol into a string.  If @buffer is too short, truncate the string.
>> - * Recommend a @maxlen of at least 32 for the longest mode, "interleave", the
>> - * longest flag, "relative", and to display at least a few node ids.
>> + * Recommend a @maxlen of at least 42 for the longest mode, "weighted
>> + * interleave", the longest flag, "balancing", and to display at least a few
>> + * node ids.
>>    */
>>   void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
>>   {
>> @@ -3331,12 +3332,15 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
>>   		p += snprintf(p, buffer + maxlen - p, "=");
>>   
>>   		/*
>> -		 * 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");
>>   	}
>>   
>>   	if (!nodes_empty(nodes))