Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 40/71] thp, memcg: split hugepage for memcg oom on cow | Date | Tue, 15 Jan 2013 14:54:37 -0800 |
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3.0-stable review patch. If anyone has any objections, please let me know.
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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 @@ -920,6 +920,8 @@ 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; } @@ -927,6 +929,7 @@ 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 @@ -3470,6 +3470,7 @@ 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) @@ -3483,13 +3484,24 @@ 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; } }
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