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mm: optimize put_mems_allowed() usage

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Since put_mems_allowed() is strictly optional, its a seqcount retry, we
don't need to evaluate the function if the allocation was in fact
successful, saving a smp_rmb some loads and comparisons on some relative
fast-paths.

Since the naming, get/put_mems_allowed() does suggest a mandatory
pairing, rename the interface, as suggested by Mel, to resemble the
seqcount interface.

This gives us: read_mems_allowed_begin() and read_mems_allowed_retry(),
where it is important to note that the return value of the latter call
is inverted from its previous incarnation.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman 2014-04-03 14:47:24 -07:00 • committed by Linus Torvalds
parent 91ca918648
commit d26914d117
8 changed files with 38 additions and 39 deletions
Download patch file Download diff file Expand all files Collapse all files

27
include/linux/cpuset.h
View file

@ -87,25 +87,26 @@ extern void rebuild_sched_domains(void);
extern void cpuset_print_task_mems_allowed(struct task_struct *p);
/*
* get_mems_allowed is required when making decisions involving mems_allowed
* such as during page allocation. mems_allowed can be updated in parallel
* and depending on the new value an operation can fail potentially causing
* process failure. A retry loop with get_mems_allowed and put_mems_allowed
* prevents these artificial failures.
* read_mems_allowed_begin is required when making decisions involving
* mems_allowed such as during page allocation. mems_allowed can be updated in
* parallel and depending on the new value an operation can fail potentially
* causing process failure. A retry loop with read_mems_allowed_begin and
* read_mems_allowed_retry prevents these artificial failures.
*/
static inline unsigned int get_mems_allowed(void)
static inline unsigned int read_mems_allowed_begin(void)
{
return read_seqcount_begin(&current->mems_allowed_seq);
}
/*
* If this returns false, the operation that took place after get_mems_allowed
* may have failed. It is up to the caller to retry the operation if
* If this returns true, the operation that took place after
* read_mems_allowed_begin may have failed artificially due to a concurrent
* update of mems_allowed. It is up to the caller to retry the operation if
* appropriate.
*/
static inline bool put_mems_allowed(unsigned int seq)
static inline bool read_mems_allowed_retry(unsigned int seq)
{
return !read_seqcount_retry(&current->mems_allowed_seq, seq);
return read_seqcount_retry(&current->mems_allowed_seq, seq);
}
static inline void set_mems_allowed(nodemask_t nodemask)
@ -225,14 +226,14 @@ static inline void set_mems_allowed(nodemask_t nodemask)
{
}
static inline unsigned int get_mems_allowed(void)
static inline unsigned int read_mems_allowed_begin(void)
{
return 0;
}
static inline bool put_mems_allowed(unsigned int seq)
static inline bool read_mems_allowed_retry(unsigned int seq)
{
return true;
return false;
}
#endif /* !CONFIG_CPUSETS */