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authorDavid Rientjes <rientjes@google.com>2012-05-29 15:06:23 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-29 16:22:19 -0700
commit1f1d06c34f7675026326cd9f39ff91e4555cf355 (patch)
treeb2493685179e3b222c915002648c3baba56318d2
parentbde8bd8a1d5242589ddcaef8e017b48b207c4729 (diff)
thp, memcg: split hugepage for memcg oom on cow
On COW, a new hugepage is allocated and charged to the memcg. If the system is oom or the charge to the memcg fails, however, the fault handler will return VM_FAULT_OOM which results in an oom kill. Instead, it's possible to fallback to splitting the hugepage so that the COW results only in an order-0 page being allocated and charged to the memcg which has a higher liklihood to succeed. This is expensive because the hugepage must be split in the page fault handler, but it is much better than unnecessarily oom killing a process. Signed-off-by: David Rientjes <rientjes@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Johannes Weiner <jweiner@redhat.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Michal Hocko <mhocko@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/huge_memory.c3
-rw-r--r--mm/memory.c18
2 files changed, 18 insertions, 3 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d7d7165156ca..edfeb8cb23df 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -952,6 +952,8 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
count_vm_event(THP_FAULT_FALLBACK);
ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
pmd, orig_pmd, page, haddr);
+ if (ret & VM_FAULT_OOM)
+ split_huge_page(page);
put_page(page);
goto out;
}
@@ -959,6 +961,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
put_page(new_page);
+ split_huge_page(page);
put_page(page);
ret |= VM_FAULT_OOM;
goto out;
diff --git a/mm/memory.c b/mm/memory.c
index 2bf9e110437c..1b7dc662bf9f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3486,6 +3486,7 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
if (unlikely(is_vm_hugetlb_page(vma)))
return hugetlb_fault(mm, vma, address, flags);
+retry:
pgd = pgd_offset(mm, address);
pud = pud_alloc(mm, pgd, address);
if (!pud)
@@ -3499,13 +3500,24 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
pmd, flags);
} else {
pmd_t orig_pmd = *pmd;
+ int ret;
+
barrier();
if (pmd_trans_huge(orig_pmd)) {
if (flags & FAULT_FLAG_WRITE &&
!pmd_write(orig_pmd) &&
- !pmd_trans_splitting(orig_pmd))
- return do_huge_pmd_wp_page(mm, vma, address,
- pmd, orig_pmd);
+ !pmd_trans_splitting(orig_pmd)) {
+ ret = do_huge_pmd_wp_page(mm, vma, address, pmd,
+ orig_pmd);
+ /*
+ * If COW results in an oom, the huge pmd will
+ * have been split, so retry the fault on the
+ * pte for a smaller charge.
+ */
+ if (unlikely(ret & VM_FAULT_OOM))
+ goto retry;
+ return ret;
+ }
return 0;
}
}