Commit 1f1d06c3 authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds

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: default avatarDavid Rientjes <rientjes@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent bde8bd8a
......@@ -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;
......
......@@ -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;
}
}
......
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