[PATCH v2 6/6] mm, mempolicy: don't check cpuset seqlock where it doesn't matter

Vlastimil Babka
2017-05-17T08:11:40Z

Two wrappers of __alloc_pages_nodemask() are checking task->mems_allowed_seq
themselves to retry allocation that has raced with a cpuset update. This has
been shown to be ineffective in preventing premature OOM's which can happen in
__alloc_pages_slowpath() long before it returns back to the wrappers to detect
the race at that level. Previous patches have made __alloc_pages_slowpath()
more robust, so we can now simply remove the seqlock checking in the wrappers
to prevent further wrong impression that it can actually help.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/mempolicy.c | 16 ----------------
1 file changed, 16 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 047181452040..7d8e56214ac0 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1898,12 +1898,9 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
struct mempolicy *pol;
struct page *page;
int preferred_nid;
- unsigned int cpuset_mems_cookie;
nodemask_t *nmask;

-retry_cpuset:
pol = get_vma_policy(vma, addr);
- cpuset_mems_cookie = read_mems_allowed_begin();

if (pol->mode == MPOL_INTERLEAVE) {
unsigned nid;
@@ -1945,8 +1942,6 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
page = __alloc_pages_nodemask(gfp, order, preferred_nid, nmask);
mpol_cond_put(pol);
out:
- if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
- goto retry_cpuset;
return page;
}

@@ -1964,23 +1959,15 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
* Allocate a page from the kernel page pool. When not in
* interrupt context and apply the current process NUMA policy.
* Returns NULL when no page can be allocated.
- *
- * Don't call cpuset_update_task_memory_state() unless
- * 1) it's ok to take cpuset_sem (can WAIT), and
- * 2) allocating for current task (not interrupt).
*/
struct page *alloc_pages_current(gfp_t gfp, unsigned order)
{
struct mempolicy *pol = &default_policy;
struct page *page;
- unsigned int cpuset_mems_cookie;

if (!in_interrupt() && !(gfp & __GFP_THISNODE))
pol = get_task_policy(current);

-retry_cpuset:
- cpuset_mems_cookie = read_mems_allowed_begin();
-
/*
* No reference counting needed for current->mempolicy
* nor system default_policy
@@ -1992,9 +1979,6 @@ struct page *alloc_pages_current(gfp_t gfp, unsigned order)
policy_node(gfp, pol, numa_node_id()),
policy_nodemask(gfp, pol));

- if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
- goto retry_cpuset;
-
return page;
}
EXPORT_SYMBOL(alloc_pages_current);
--
2.12.2