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[Qemu-devel] [PATCH 09/23] userfaultfd: prevent khugepaged to merge if u
From: |
Andrea Arcangeli |
Subject: |
[Qemu-devel] [PATCH 09/23] userfaultfd: prevent khugepaged to merge if userfaultfd is armed |
Date: |
Thu, 14 May 2015 19:31:06 +0200 |
If userfaultfd is armed on a certain vma we can't "fill" the holes
with zeroes or we'll break the userland on demand paging. The holes if
the userfault is armed, are really missing information (not zeroes)
that the userland has to load from network or elsewhere.
The same issue happens for wrprotected ptes that we can't just convert
into a single writable pmd_trans_huge.
We could however in theory still merge across zeropages if only
VM_UFFD_MISSING is set (so if VM_UFFD_WP is not set)... that could be
slightly improved but it'd be much more complex code for a tiny corner
case.
Signed-off-by: Andrea Arcangeli <address@hidden>
---
mm/huge_memory.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c221be3..9671f51 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2198,7 +2198,8 @@ static int __collapse_huge_page_isolate(struct
vm_area_struct *vma,
_pte++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
- if (++none_or_zero <= khugepaged_max_ptes_none)
+ if (!userfaultfd_armed(vma) &&
+ ++none_or_zero <= khugepaged_max_ptes_none)
continue;
else
goto out;
@@ -2651,7 +2652,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
_pte++, _address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
- if (++none_or_zero <= khugepaged_max_ptes_none)
+ if (!userfaultfd_armed(vma) &&
+ ++none_or_zero <= khugepaged_max_ptes_none)
continue;
else
goto out_unmap;
- [Qemu-devel] [PATCH 18/23] userfaultfd: buildsystem activation, (continued)
- [Qemu-devel] [PATCH 18/23] userfaultfd: buildsystem activation, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 20/23] userfaultfd: UFFDIO_COPY|UFFDIO_ZEROPAGE uAPI, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 19/23] userfaultfd: activate syscall, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 21/23] userfaultfd: mcopy_atomic|mfill_zeropage: UFFDIO_COPY|UFFDIO_ZEROPAGE preparation, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 03/23] userfaultfd: uAPI, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 17/23] userfaultfd: solve the race between UFFDIO_COPY|ZEROPAGE and read, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 06/23] userfaultfd: add VM_UFFD_MISSING and VM_UFFD_WP, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 04/23] userfaultfd: linux/userfaultfd_k.h, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 12/23] userfaultfd: Rename uffd_api.bits into .features fixup, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 11/23] userfaultfd: Rename uffd_api.bits into .features, Andrea Arcangeli, 2015/05/14
- [Qemu-devel] [PATCH 09/23] userfaultfd: prevent khugepaged to merge if userfaultfd is armed,
Andrea Arcangeli <=
- [Qemu-devel] [PATCH 22/23] userfaultfd: avoid mmap_sem read recursion in mcopy_atomic, Andrea Arcangeli, 2015/05/14
[Qemu-devel] [PATCH 14/23] userfaultfd: wake pending userfaults, Andrea Arcangeli, 2015/05/14
[Qemu-devel] [PATCH 02/23] userfaultfd: waitqueue: add nr wake parameter to __wake_up_locked_key, Andrea Arcangeli, 2015/05/14
[Qemu-devel] [PATCH 08/23] userfaultfd: teach vma_merge to merge across vma->vm_userfaultfd_ctx, Andrea Arcangeli, 2015/05/14
[Qemu-devel] [PATCH 07/23] userfaultfd: call handle_userfault() for userfaultfd_missing() faults, Andrea Arcangeli, 2015/05/14
[Qemu-devel] [PATCH 13/23] userfaultfd: change the read API to return a uffd_msg, Andrea Arcangeli, 2015/05/14