# Re: \[PATCH\] vfs: cap dedupe request structure size at PAGE\_SIZE

- From: Mark Fasheh \<hidden\>
- Date: 2016-08-02 05:35:17 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/08/111171
- Thread: https://ratatoskr.run/linux-api/2016/07/109679/t.md

```text
On Thu, Jul 28, 2016 at 11:35:34AM -0700, Darrick J. Wong wrote:
> Kirill A. Shutemov reports that the kernel doesn't try to cap dest_count
> in any way, and uses the number to allocate kernel memory.  This causes
> high order allocation warnings in the kernel log if someone passes in a
> big enough value.  We should clamp the allocation at PAGE_SIZE to avoid
> stressing the VM.
> 
> The two existing users of the dedupe ioctl never send more than 120
> requests, so we can safely clamp dest_range at PAGE_SIZE, because with
> 4k pages we can handle up to 127 dedupe candidates.  Given the max
> extent length of 16MB, we can end up doing 2GB of IO which is plenty.
> 
> Reported-by: "Kirill A. Shutemov" <redacted>
> Signed-off-by: Darrick J. Wong <redacted>

Reviewed-by: Mark Fasheh <redacted>

--
Mark Fasheh

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