[ 065/171] thp, memcg: split hugepage for memcg oom on cow

Greg Kroah-Hartman
2013-01-15T23:45:14Z

From: David Rientjes <rientjes@google.com>

commit 1f1d06c34f7675026326cd9f39ff91e4555cf355 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/huge_memory.c | 3 +++
mm/memory.c | 18 +++++++++++++++---
2 files changed, 18 insertions(+), 3 deletions(-)

--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -950,6 +950,8 @@ int do_huge_pmd_wp_page(struct mm_struct
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;
}
@@ -957,6 +959,7 @@ int do_huge_pmd_wp_page(struct mm_struct

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;
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3494,6 +3494,7 @@ int handle_mm_fault(struct mm_struct *mm
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)
@@ -3507,13 +3508,24 @@ int handle_mm_fault(struct mm_struct *mm
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;
}
}