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Date: Mon, 26 Mar 2012 18:20:52 +0200
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: Mel Gorman <mgorman@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Miao Xie <miaox@...fujitsu.com>,
David Rientjes <rientjes@...gle.com>,
Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpuset: mm: Reduce large amounts of memory barrier
related damage v3
On Mon, 2012-03-26 at 16:50 +0100, Mel Gorman wrote:
> On Mon, Mar 26, 2012 at 12:56:24PM +0200, Peter Zijlstra wrote:
> > On Wed, 2012-03-07 at 18:08 +0000, Mel Gorman wrote:
> > > + } while (!put_mems_allowed(cpuset_mems_cookie) && !page);
> >
> > Sorry for only noticing this now, but wouldn't it be better to first
> > check page and only then bother with the put_mems_allowed() thing? That
> > avoids the smp_rmb() and seqcount conditional all together in the likely
> > case the allocation actually succeeded.
> >
> > <SNIP>
> >
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index c3811bc..3b41553 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -504,7 +504,7 @@ struct page *__page_cache_alloc(gfp_t gfp)
> > cpuset_mems_cookie = get_mems_allowed();
> > n = cpuset_mem_spread_node();
> > page = alloc_pages_exact_node(n, gfp, 0);
> > - } while (!put_mems_allowed(cpuset_mems_cookie) && !page);
> > + } while (!page && !put_mems_allowed(cpuset_mems_cookie));
> >
> > return page;
> > }
>
> I think such a change would be better but should also rename the API.
> If developers see a get_foo type call, they will expect to see a put_foo
> call or assume it's a bug even though the implementation happens to be ok
> with that. Any suggestion on what a good new name would be?
>
> How about read_mems_allowed_begin() and read_mems_allowed_retry()?
>
> read_mems_allowed_begin would be a rename of get_mems_allowed(). In an
> error path, read_mems_allowed_retry() would documented to be *optionally*
> called when deciding whether to retry the operation or not. In this scheme,
> !put_mems_allowed would become read_mems_allowed_retry() which might be
> a bit easier to read overall.
One:
git grep -l "\(get\|put\)_mems_allowed" | while read file; do sed -i -e
's/\<get_mems_allowed\>/read_mems_allowed_begin/g' -e
's/\<put_mems_allowed\>/read_mems_allowed_retry/g' $file; done
and a few edits later..
---
include/linux/cpuset.h | 18 +++++++++---------
kernel/cpuset.c | 2 +-
mm/filemap.c | 4 ++--
mm/hugetlb.c | 4 ++--
mm/mempolicy.c | 14 +++++++-------
mm/page_alloc.c | 8 ++++----
mm/slab.c | 4 ++--
mm/slub.c | 16 +++-------------
8 files changed, 30 insertions(+), 40 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 7a7e5fd..d008b03 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -89,25 +89,25 @@ 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
+ * 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 get_mems_allowed and put_mems_allowed
+ * 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(¤t->mems_allowed_seq);
}
/*
- * If this returns false, the operation that took place after get_mems_allowed
+ * If this returns false, the operation that took place after read_mems_allowed_begin
* may have failed. 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(¤t->mems_allowed_seq, seq);
+ return read_seqcount_retry(¤t->mems_allowed_seq, seq);
}
static inline void set_mems_allowed(nodemask_t nodemask)
@@ -225,14 +225,14 @@ 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 */
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 1010cc6..703df59 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -976,7 +976,7 @@ 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.
*/
diff --git a/mm/filemap.c b/mm/filemap.c
index c3811bc..5694807 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -501,10 +501,10 @@ 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;
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b8ce6f4..6c52f6a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -541,7 +541,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
unsigned int cpuset_mems_cookie;
retry_cpuset:
- cpuset_mems_cookie = get_mems_allowed();
+ cpuset_mems_cookie = read_mems_allowed_begin();
zonelist = huge_zonelist(vma, address,
htlb_alloc_mask, &mpol, &nodemask);
/*
@@ -570,7 +570,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
}
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;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index cfb6c86..ee5f48c 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1692,7 +1692,7 @@ 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,
@@ -1857,7 +1857,7 @@ 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;
@@ -1865,7 +1865,7 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
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;
@@ -1878,7 +1878,7 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
struct page *page = __alloc_pages_nodemask(gfp, order,
zl, policy_nodemask(gfp, 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;
}
@@ -1887,7 +1887,7 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
*/
page = __alloc_pages_nodemask(gfp, order, zl,
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;
}
@@ -1921,7 +1921,7 @@ 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
@@ -1934,7 +1934,7 @@ struct page *alloc_pages_current(gfp_t gfp, unsigned order)
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;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index caea788..b586d96 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2402,7 +2402,7 @@ __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,
@@ -2429,7 +2429,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
* 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;
return page;
@@ -2651,9 +2651,9 @@ 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;
}
diff --git a/mm/slab.c b/mm/slab.c
index 29c8716..e5a4533 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3318,7 +3318,7 @@ 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(current->mempolicy), flags);
retry:
@@ -3374,7 +3374,7 @@ static void *fallback_alloc(struct kmem_cache *cache, gfp_t flags)
}
}
- if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !obj))
+ if (unlikely(!obj && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;
return obj;
}
diff --git a/mm/slub.c b/mm/slub.c
index f4a6229..7a158be 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1606,7 +1606,7 @@ static struct page *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(current->mempolicy), flags);
for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
struct kmem_cache_node *n;
@@ -1616,21 +1616,11 @@ static struct page *get_any_partial(struct kmem_cache *s, gfp_t flags,
if (n && cpuset_zone_allowed_hardwall(zone, flags) &&
n->nr_partial > s->min_partial) {
object = get_partial_node(s, n, c);
- 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.
- */
- put_mems_allowed(cpuset_mems_cookie);
+ if (object)
return object;
- }
}
}
- } while (!put_mems_allowed(cpuset_mems_cookie));
+ } while (read_mems_allowed_retry(cpuset_mems_cookie));
#endif
return NULL;
}
--
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