Messages in this thread | | | Date | Tue, 25 Jul 2017 01:14:00 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v5 1/5] mm: add vm_insert_mixed_mkwrite() |
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On Mon, Jul 24, 2017 at 11:06:12AM -0600, Ross Zwisler wrote: > @@ -1658,14 +1658,35 @@ static int insert_pfn(struct vm_area_struct *vma, unsigned long addr, > if (!pte) > goto out; > retval = -EBUSY; > - if (!pte_none(*pte)) > - goto out_unlock; > + if (!pte_none(*pte)) { > + if (mkwrite) { > + /* > + * For read faults on private mappings the PFN passed > + * in may not match the PFN we have mapped if the > + * mapped PFN is a writeable COW page. In the mkwrite > + * case we are creating a writable PTE for a shared > + * mapping and we expect the PFNs to match. > + */
Can we?
I guess it's up to filesystem if it wants to reuse the same spot to write data or not. I think your assumptions works for ext4 and xfs. I wouldn't be that sure for btrfs or other filesystems with CoW support.
-- Kirill A. Shutemov
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