Hello,
On Thu, Dec 22, 2016 at 11:17:13AM +0300, Kirill A. Shutemov wrote:
< snip >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 36c774f..7408ddc 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -3637,18 +3637,20 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> > if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
> > return do_huge_pmd_numa_page(&vmf, orig_pmd);
> >
> > - if ((vmf.flags & FAULT_FLAG_WRITE) &&
> > - !pmd_write(orig_pmd)) {
> > - ret = wp_huge_pmd(&vmf, orig_pmd);
> > - if (!(ret & VM_FAULT_FALLBACK))
> > + if (vmf.flags & FAULT_FLAG_WRITE) {
> > + if (!pmd_write(orig_pmd)) {
> > + ret = wp_huge_pmd(&vmf, orig_pmd);
> > + if (ret == VM_FAULT_FALLBACK)
>
> In theory, more than one flag can be set and it would lead to
> false-negative. Bit check was the right thing.
>
> And I don't understand why do you need to change code in
> __handle_mm_fault() at all.
> From what I see change to huge_pmd_set_accessed() should be enough.
Yeb. Thanks for the review. Here v2 goes.
>From b3ec95c0df91ad113525968a4a6b53030fd0b48d Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Thu, 22 Dec 2016 23:43:49 +0900
Subject: [PATCH v2] mm: pmd dirty emulation in page fault handler
Andreas reported [1] made a test in jemalloc hang in THP mode in arm64.
http://lkml.kernel.org/r/mvmmvfy37g1.fsf@xxxxxxxxxxxxxxx
The problem is page fault handler supports only accessed flag emulation
for THP page of SW-dirty/accessed architecture.
This patch enables dirty-bit emulation for those architectures.
Without it, MADV_FREE makes application hang by repeated fault forever.
[1] b8d3c4c3009d, mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called
Cc: Jason Evans <je@xxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx> [4.5+]
Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called")
Reported-by: Andreas Schwab <schwab@xxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
* from v1
* Remove __handle_mm_fault part - Kirill
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 10eedbf..29ec8a4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -883,15 +883,17 @@ void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
{
pmd_t entry;
unsigned long haddr;
+ bool write = vmf->flags & FAULT_FLAG_WRITE;
vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
goto unlock;
entry = pmd_mkyoung(orig_pmd);
+ if (write)
+ entry = pmd_mkdirty(entry);
haddr = vmf->address & HPAGE_PMD_MASK;
- if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry,
- vmf->flags & FAULT_FLAG_WRITE))
+ if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write))
update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd);
unlock:
--
2.7.4
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