Re: Dirty/Access bits vs. page content

[Dave Hansen <dave.hansen@intel.com>]

On 04/25/2014 11:41 AM, Hugh Dickins wrote:
> On Fri, 25 Apr 2014, Dave Hansen wrote:
>> On 04/25/2014 05:01 AM, Hugh Dickins wrote:
>>> Er, i_mmap_mutex.
>>>
>>> That's what unmap_mapping_range(), and page_mkclean()'s rmap_walk,
>>> take to iterate over the file vmas.  So perhaps there's no race at all
>>> in the unmap_mapping_range() case.  And easy (I imagine) to fix the
>>> race in Dave's racewrite.c use of MADV_DONTNEED: untested patch below.
>>>
>>> But exit and munmap() don't take i_mmap_mutex: perhaps they should
>>> when encountering a VM_SHARED vma (I believe VM_SHARED should be
>>> peculiar to having vm_file set, but test both below because I don't
>>> want to oops in some odd corner where a special vma is set up).
>>
>> Hey Hugh,
>>
>> Do you want some testing on this?
> 
> Yes, please do: I just haven't gotten around to cloning the git
> tree and trying it.  It's quite likely that we shall go Linus's
> way rather than this, but still useful to have the information
> as to whether this way really is viable.

Your patch works fine for the madvise() case.  The effect appears the
same as Linus's to my test case at least.  I didn't test any unmaps or
other creative uses of unmap_mapping_range().

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