The patch titled
Subject: userfaultfd: prevent khugepaged to merge if userfaultfd is armed
has been removed from the -mm tree. Its filename was
userfaultfd-prevent-khugepaged-to-merge-if-userfaultfd-is-armed.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: userfaultfd: prevent khugepaged to merge if userfaultfd is armed
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 <aarcange@xxxxxxxxxx>
Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: Sanidhya Kashyap <sanidhya.gatech@xxxxxxxxx>
Cc: zhang.zhanghailiang@xxxxxxxxxx
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Andres Lagar-Cavilla <andreslc@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Peter Feiner <pfeiner@xxxxxxxxxx>
Cc: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: "Huangpeng (Peter)" <peter.huangpeng@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN mm/huge_memory.c~userfaultfd-prevent-khugepaged-to-merge-if-userfaultfd-is-armed mm/huge_memory.c
--- a/mm/huge_memory.c~userfaultfd-prevent-khugepaged-to-merge-if-userfaultfd-is-armed
+++ a/mm/huge_memory.c
@@ -2158,7 +2158,8 @@ static int __collapse_huge_page_isolate(
_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;
@@ -2611,7 +2612,8 @@ static int khugepaged_scan_pmd(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;
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
userfaultfd-selftest-update-userfaultfd-x86-32bit-syscall-number.patch
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