diff mbox

[PATCHv6,06/37] thp: handle write-protection faults for file THP

Message ID 20170126115819.58875-7-kirill.shutemov@linux.intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Kirill A . Shutemov Jan. 26, 2017, 11:57 a.m. UTC 
For filesystems that wants to be write-notified (has mkwrite), we will
encount write-protection faults for huge PMDs in shared mappings.

The easiest way to handle them is to clear the PMD and let it refault as
wriable.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 mm/memory.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

Comments

Matthew Wilcox Jan. 26, 2017, 3:44 p.m. UTC | #1 
On Thu, Jan 26, 2017 at 02:57:48PM +0300, Kirill A. Shutemov wrote:
> For filesystems that wants to be write-notified (has mkwrite), we will
> encount write-protection faults for huge PMDs in shared mappings.
> 
> The easiest way to handle them is to clear the PMD and let it refault as
> wriable.

... of course, the filesystem could implement ->pmd_fault, and then it
wouldn't hit this case ...
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Kirill A. Shutemov Jan. 26, 2017, 3:57 p.m. UTC | #2 
On Thu, Jan 26, 2017 at 07:44:39AM -0800, Matthew Wilcox wrote:
> On Thu, Jan 26, 2017 at 02:57:48PM +0300, Kirill A. Shutemov wrote:
> > For filesystems that wants to be write-notified (has mkwrite), we will
> > encount write-protection faults for huge PMDs in shared mappings.
> > 
> > The easiest way to handle them is to clear the PMD and let it refault as
> > wriable.
> 
> ... of course, the filesystem could implement ->pmd_fault, and then it
> wouldn't hit this case ...

I would rather get rid of ->pmd_fault/->huge_fault :)

->fault should be flexible enough to provide for all of them...
Matthew Wilcox Feb. 9, 2017, 8:19 p.m. UTC | #3 
On Thu, Jan 26, 2017 at 02:57:48PM +0300, Kirill A. Shutemov wrote:
> For filesystems that wants to be write-notified (has mkwrite), we will
> encount write-protection faults for huge PMDs in shared mappings.
> 
> The easiest way to handle them is to clear the PMD and let it refault as
> wriable.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Jan Kara <jack@suse.cz>

Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
diff mbox

Patch

diff --git a/mm/memory.c b/mm/memory.c
index 6bf2b471e30c..903d9d3e01c0 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3488,8 +3488,16 @@  static int wp_huge_pmd(struct vm_fault *vmf, pmd_t orig_pmd)
 		return vmf->vma->vm_ops->pmd_fault(vmf->vma, vmf->address,
 						   vmf->pmd, vmf->flags);
 
+	if (vmf->vma->vm_flags & VM_SHARED) {
+		/* Clear PMD */
+		zap_page_range_single(vmf->vma, vmf->address & HPAGE_PMD_MASK,
+				HPAGE_PMD_SIZE, NULL);
+
+		/* Refault to establish writable PMD */
+		return 0;
+	}
+
 	/* COW handled on pte level: split pmd */
-	VM_BUG_ON_VMA(vmf->vma->vm_flags & VM_SHARED, vmf->vma);
 	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
 
 	return VM_FAULT_FALLBACK;