Re: [PATCH] mm/numa_balancing: Teach mpol_to_str about the balancing mode

[Tvrtko Ursulin]

On 26/06/2024 09:48, Huang, Ying wrote:
> Tvrtko Ursulin <tursulin@xxxxxxxxxx> writes:
>
> > From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>
> >
> > 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text of bda420b98505 said, which is probably outdated.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@xxxxxxxxx>

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@xxxxxxxxxx>
> > References: bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes")
> > Cc: Huang Ying <ying.huang@xxxxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Rik van Riel <riel@xxxxxxxxxxx>
> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> > Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> > Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > Cc: Michal Hocko <mhocko@xxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > ---
> >   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))