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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
Show Stats 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 */

2
kernel/cpuset.c
View File

@ -1022,7 +1022,7 @@ static void cpuset_change_task_nodemask(struct task_struct *tsk,
task_lock(tsk);
/*
* Determine if a loop is necessary if another thread is doing
* get_mems_allowed(). If at least one node remains unchanged and
* read_mems_allowed_begin(). If at least one node remains unchanged and
* tsk does not have a mempolicy, then an empty nodemask will not be
* possible when mems_allowed is larger than a word.
*/

4
mm/filemap.c
View File

@ -520,10 +520,10 @@ struct page *__page_cache_alloc(gfp_t gfp)
if (cpuset_do_page_mem_spread()) {
unsigned int cpuset_mems_cookie;
do {
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
n = cpuset_mem_spread_node();
page = alloc_pages_exact_node(n, gfp, 0);
} while (!put_mems_allowed(cpuset_mems_cookie) && !page);
} while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
return page;
}

4
mm/hugetlb.c
View File

@ -540,7 +540,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
goto err;
retry_cpuset:
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
zonelist = huge_zonelist(vma, address,
htlb_alloc_mask(h), &mpol, &nodemask);
@ -562,7 +562,7 @@ retry_cpuset:
}
mpol_cond_put(mpol);
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;

12
mm/mempolicy.c
View File

@ -1899,7 +1899,7 @@ int node_random(const nodemask_t *maskp)
* If the effective policy is 'BIND, returns a pointer to the mempolicy's
* @nodemask for filtering the zonelist.
*
* Must be protected by get_mems_allowed()
* Must be protected by read_mems_allowed_begin()
*/
struct zonelist *huge_zonelist(struct vm_area_struct *vma, unsigned long addr,
gfp_t gfp_flags, struct mempolicy **mpol,
@ -2063,7 +2063,7 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
retry_cpuset:
pol = get_vma_policy(current, vma, addr);
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
if (unlikely(pol->mode == MPOL_INTERLEAVE)) {
unsigned nid;
@ -2071,7 +2071,7 @@ retry_cpuset:
nid = interleave_nid(pol, vma, addr, PAGE_SHIFT + order);
mpol_cond_put(pol);
page = alloc_page_interleave(gfp, order, nid);
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;
@ -2081,7 +2081,7 @@ retry_cpuset:
policy_nodemask(gfp, pol));
if (unlikely(mpol_needs_cond_ref(pol)))
__mpol_put(pol);
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;
}
@ -2115,7 +2115,7 @@ struct page *alloc_pages_current(gfp_t gfp, unsigned order)
pol = &default_policy;
retry_cpuset:
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
/*
* No reference counting needed for current->mempolicy
@ -2128,7 +2128,7 @@ retry_cpuset:
policy_zonelist(gfp, pol, numa_node_id()),
policy_nodemask(gfp, pol));
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return page;

8
mm/page_alloc.c
View File

@ -2739,7 +2739,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
return NULL;
retry_cpuset:
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
/* The preferred zone is used for statistics later */
first_zones_zonelist(zonelist, high_zoneidx,
@ -2777,7 +2777,7 @@ out:
* the mask is being updated. If a page allocation is about to fail,
* check if the cpuset changed during allocation and if so, retry.
*/
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
memcg_kmem_commit_charge(page, memcg, order);
@ -3045,9 +3045,9 @@ bool skip_free_areas_node(unsigned int flags, int nid)
goto out;
do {
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
ret = !node_isset(nid, cpuset_current_mems_allowed);
} while (!put_mems_allowed(cpuset_mems_cookie));
} while (read_mems_allowed_retry(cpuset_mems_cookie));
out:
return ret;
}

4
mm/slab.c
View File

@ -3073,7 +3073,7 @@ static void *fallback_alloc(struct kmem_cache *cache, gfp_t flags)
local_flags = flags & (GFP_CONSTRAINT_MASK|GFP_RECLAIM_MASK);
retry_cpuset:
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
zonelist = node_zonelist(slab_node(), flags);
retry:
@ -3131,7 +3131,7 @@ retry:
}
}
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !obj))
if (unlikely(!obj && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return obj;
}

16
mm/slub.c
View File

@ -1684,7 +1684,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
return NULL;
do {
cpuset_mems_cookie = get_mems_allowed();
cpuset_mems_cookie = read_mems_allowed_begin();
zonelist = node_zonelist(slab_node(), flags);
for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
struct kmem_cache_node *n;
@ -1696,19 +1696,17 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
object = get_partial_node(s, n, c, flags);
if (object) {
/*
* Return the object even if
* put_mems_allowed indicated that
* the cpuset mems_allowed was
* updated in parallel. It's a
* harmless race between the alloc
* and the cpuset update.
* Don't check read_mems_allowed_retry()
* here - if mems_allowed was updated in
* parallel, that was a harmless race
* between allocation and the cpuset
* update
*/
put_mems_allowed(cpuset_mems_cookie);
return object;
}
}
}
} while (!put_mems_allowed(cpuset_mems_cookie));
} while (read_mems_allowed_retry(cpuset_mems_cookie));
#endif
return NULL;
}