On Mon 24-08-15 13:09:43, Mel Gorman wrote:
> David Rientjes correctly pointed out that the "root cpuset may not exclude
> mems on the system so, even if mounted, there's no need to check or be
> worried about concurrent change when there is only one cpuset".
Hmm, but cpuset_inc() is called only from cpuset_css_online and only
when it is called with non-NULL css->parent AFAICS. This means that the
static key should be still false after the root cpuset is created.
> The three checks for cpusets_enabled() care whether a cpuset exists that
> can limit memory, not that cpuset is enabled as such. This patch replaces
> cpusets_enabled() with cpusets_mems_enabled() which checks if at least one
> cpuset exists that can limit memory and updates the appropriate call sites.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
> include/linux/cpuset.h | 16 +++++++++-------
> mm/page_alloc.c | 2 +-
> 2 files changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 6eb27cb480b7..1e823870987e 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -17,10 +17,6 @@
> #ifdef CONFIG_CPUSETS
>
> extern struct static_key cpusets_enabled_key;
> -static inline bool cpusets_enabled(void)
> -{
> - return static_key_false(&cpusets_enabled_key);
> -}
>
> static inline int nr_cpusets(void)
> {
> @@ -28,6 +24,12 @@ static inline int nr_cpusets(void)
> return static_key_count(&cpusets_enabled_key) + 1;
> }
>
> +/* Returns true if a cpuset exists that can set cpuset.mems */
> +static inline bool cpusets_mems_enabled(void)
> +{
> + return nr_cpusets() > 1;
> +}
> +
> static inline void cpuset_inc(void)
> {
> static_key_slow_inc(&cpusets_enabled_key);
> @@ -104,7 +106,7 @@ extern void cpuset_print_task_mems_allowed(struct task_struct *p);
> */
> static inline unsigned int read_mems_allowed_begin(void)
> {
> - if (!cpusets_enabled())
> + if (!cpusets_mems_enabled())
> return 0;
>
> return read_seqcount_begin(¤t->mems_allowed_seq);
> @@ -118,7 +120,7 @@ static inline unsigned int read_mems_allowed_begin(void)
> */
> static inline bool read_mems_allowed_retry(unsigned int seq)
> {
> - if (!cpusets_enabled())
> + if (!cpusets_mems_enabled())
> return false;
>
> return read_seqcount_retry(¤t->mems_allowed_seq, seq);
> @@ -139,7 +141,7 @@ static inline void set_mems_allowed(nodemask_t nodemask)
>
> #else /* !CONFIG_CPUSETS */
>
> -static inline bool cpusets_enabled(void) { return false; }
> +static inline bool cpusets_mems_enabled(void) { return false; }
>
> static inline int cpuset_init(void) { return 0; }
> static inline void cpuset_init_smp(void) {}
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 62ae28d8ae8d..2c1c3bf54d15 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2470,7 +2470,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> if (IS_ENABLED(CONFIG_NUMA) && zlc_active &&
> !zlc_zone_worth_trying(zonelist, z, allowednodes))
> continue;
> - if (cpusets_enabled() &&
> + if (cpusets_mems_enabled() &&
> (alloc_flags & ALLOC_CPUSET) &&
> !cpuset_zone_allowed(zone, gfp_mask))
> continue;
> --
> 2.4.6
--
Michal Hocko
SUSE Labs
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