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SubjectRe: [PATCH v3] mm/page_alloc: detect allocation forbidden by cpuset and bail out early
On Tue, 14 Sep 2021, Feng Tang wrote:

> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index d2b9c41..d58e047 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -34,6 +34,8 @@
> */
> extern struct static_key_false cpusets_pre_enable_key;
> extern struct static_key_false cpusets_enabled_key;
> +extern struct static_key_false cpusets_insane_config_key;
> +
> static inline bool cpusets_enabled(void)
> {
> return static_branch_unlikely(&cpusets_enabled_key);
> @@ -51,6 +53,19 @@ static inline void cpuset_dec(void)
> static_branch_dec_cpuslocked(&cpusets_pre_enable_key);
> }
>
> +/*
> + * This will get enabled whenever a cpuset configuration is considered
> + * unsupportable in general. E.g. movable only node which cannot satisfy
> + * any non movable allocations (see update_nodemask). Page allocator
> + * needs to make additional checks for those configurations and this
> + * check is meant to guard those checks without any overhead for sane
> + * configurations.
> + */
> +static inline bool cpusets_insane_config(void)
> +{
> + return static_branch_unlikely(&cpusets_insane_config_key);
> +}
> +
> extern int cpuset_init(void);
> extern void cpuset_init_smp(void);
> extern void cpuset_force_rebuild(void);
> @@ -167,6 +182,8 @@ static inline void set_mems_allowed(nodemask_t nodemask)
>
> static inline bool cpusets_enabled(void) { return false; }
>
> +static inline bool cpusets_insane_config(void) { return false; }
> +
> static inline int cpuset_init(void) { return 0; }
> static inline void cpuset_init_smp(void) {}
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 6a1d79d..a455333 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1220,6 +1220,22 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
> #define for_each_zone_zonelist(zone, z, zlist, highidx) \
> for_each_zone_zonelist_nodemask(zone, z, zlist, highidx, NULL)
>
> +/* Whether the 'nodes' are all movable nodes */
> +static inline bool movable_only_nodes(nodemask_t *nodes)
> +{
> + struct zonelist *zonelist;
> + struct zoneref *z;
> +
> + if (nodes_empty(*nodes))
> + return false;
> +
> + zonelist =
> + &NODE_DATA(first_node(*nodes))->node_zonelists[ZONELIST_FALLBACK];
> + z = first_zones_zonelist(zonelist, ZONE_NORMAL, nodes);
> + return (!z->zone) ? true : false;
> +}
> +
> +
> #ifdef CONFIG_SPARSEMEM
> #include <asm/sparsemem.h>
> #endif
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index df1ccf4..7fa633e 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -69,6 +69,13 @@
> DEFINE_STATIC_KEY_FALSE(cpusets_pre_enable_key);
> DEFINE_STATIC_KEY_FALSE(cpusets_enabled_key);
>
> +/*
> + * There could be abnormal cpuset configurations for cpu or memory
> + * node binding, add this key to provide a quick low-cost judgement
> + * of the situation.
> + */
> +DEFINE_STATIC_KEY_FALSE(cpusets_insane_config_key);
> +
> /* See "Frequency meter" comments, below. */
>
> struct fmeter {
> @@ -1868,6 +1875,14 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
> if (retval < 0)
> goto done;
>
> + if (!cpusets_insane_config() &&
> + movable_only_nodes(&trialcs->mems_allowed)) {
> + static_branch_enable(&cpusets_insane_config_key);
> + pr_info("Unsupported (movable nodes only) cpuset configuration detected (nmask=%*pbl)! "
> + "Cpuset allocations might fail even with a lot of memory available.\n",
> + nodemask_pr_args(&trialcs->mems_allowed));
> + }
> +
> spin_lock_irq(&callback_lock);
> cs->mems_allowed = trialcs->mems_allowed;
> spin_unlock_irq(&callback_lock);

Is this the only time that the state of the nodemask may change?

I'm wondering about a single node nodemask, for example, where all
ZONE_NORMAL memory is hot-removed.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b37435c..a7e0854 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4914,6 +4914,19 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> if (!ac->preferred_zoneref->zone)
> goto nopage;
>
> + /*
> + * Check for insane configurations where the cpuset doesn't contain
> + * any suitable zone to satisfy the request - e.g. non-movable
> + * GFP_HIGHUSER allocations from MOVABLE nodes only.
> + */
> + if (cpusets_insane_config() && (gfp_mask & __GFP_HARDWALL)) {
> + struct zoneref *z = first_zones_zonelist(ac->zonelist,
> + ac->highest_zoneidx,
> + &cpuset_current_mems_allowed);
> + if (!z->zone)
> + goto nopage;
> + }
> +
> if (alloc_flags & ALLOC_KSWAPD)
> wake_all_kswapds(order, gfp_mask, ac);
>

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