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Message-ID: <874j90eiuy.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Mon, 08 Jul 2024 10:08:05 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Tvrtko Ursulin <tursulin@...lia.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
kernel-dev@...lia.com, Tvrtko Ursulin <tvrtko.ursulin@...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>, stable@...r.kernel.org
Subject: Re: [PATCH 1/3] mm/numa_balancing: Teach mpol_to_str about the
balancing mode
Tvrtko Ursulin <tursulin@...lia.com> writes:
> From: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
>
> Since balancing mode was added in
> bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes"),
> it was possible to set this mode but it wouldn't be shown in
> /proc/<pid>/numa_maps since there was no support for it in the
> mpol_to_str() helper.
>
> Furthermore, because the balancing mode sets the MPOL_F_MORON flag, it
> would be displayed as 'default' due a workaround introduced a few years
> earlier in
> 8790c71a18e5 ("mm/mempolicy.c: fix mempolicy printing in numa_maps").
>
> To tidy this up we implement two changes:
>
> Replace the MPOL_F_MORON check by pointer comparison against the
> preferred_node_policy array. By doing this we generalise the current
> special casing and replace the incorrect 'default' with the correct
> 'bind' for the mode.
>
> Secondly, we add a string representation and corresponding handling for
> the MPOL_F_NUMA_BALANCING flag.
>
> With the two changes together we start showing the balancing flag when it
> is set and therefore complete the fix.
>
> Representation format chosen is to separate multiple flags with vertical
> bars, following what existed long time ago in kernel 2.6.25. But as
> between then and now there wasn't a way to display multiple flags, this
> patch does not change the format in practice.
>
> Some /proc/<pid>/numa_maps output examples:
>
> 555559580000 bind=balancing:0-1,3 file=...
> 555585800000 bind=balancing|static:0,2 file=...
> 555635240000 prefer=relative:0 file=
>
> v2:
> * Fully fix by introducing MPOL_F_KERNEL.
>
> v3:
> * Abandoned the MPOL_F_KERNEL approach in favour of pointer comparisons.
> * Removed lookup generalisation for easier backporting.
> * Replaced commas as separator with vertical bars.
> * Added a few more words about the string format in the commit message.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
> Fixes: bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes")
> References: 8790c71a18e5 ("mm/mempolicy.c: fix mempolicy printing in numa_maps")
> 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>
> Cc: <stable@...r.kernel.org> # v5.12+
> ---
> mm/mempolicy.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index aec756ae5637..1bfb6c73a39c 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
And we may display 2 flags now, +9 further?
> + * node ids.
> */
> void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
> {
> @@ -3303,7 +3304,10 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
> unsigned short mode = MPOL_DEFAULT;
> unsigned short flags = 0;
>
> - if (pol && pol != &default_policy && !(pol->flags & MPOL_F_MORON)) {
> + if (pol &&
> + pol != &default_policy &&
> + !(pol >= &preferred_node_policy[0] &&
> + pol <= &preferred_node_policy[MAX_NUMNODES - 1])) {
Better to replace MAX_NUMNODES with ARRAY_SIZE() here.
> mode = pol->mode;
> flags = pol->flags;
> }
> @@ -3331,12 +3335,18 @@ 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
> + * Static and relative 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) {
> + if (hweight16(flags & MPOL_MODE_FLAGS) > 1)
> + p += snprintf(p, buffer + maxlen - p, "|");
> + p += snprintf(p, buffer + maxlen - p, "balancing");
> + }
Still think that it's better to move this part to [2/3]. Unless you can
make the change small and the resulting code looks good.
> }
>
> if (!nodes_empty(nodes))
--
Best Regards,
Huang, Ying
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