Re: [PATCH 1/3] mm(v4.1): New pfn_mkwrite same as page_mkwrite for VM_PFNMAP

[Boaz Harrosh <boaz@plexistor.com>]

On 04/07/2015 12:03 PM, Kirill A. Shutemov wrote:
> On Tue, Apr 07, 2015 at 11:40:06AM +0300, Boaz Harrosh wrote:
>>
>> [v2]
>> Based on linux-next/akpm [3dc4623]. For v4.1 merge window
>> Incorporated comments from Andrew And Kirill
> 
> Not really. You've ignored most of them. See below.
> 

Yes sorry about that I sent the wrong version.

<>
>> ---
>>  include/linux/mm.h |  3 +++
>>  mm/memory.c        | 35 +++++++++++++++++++++++++++++++----
> 
> Please, document it in Documentation/filesystems/Locking.
> 

Ha, I missed this one. Ok will try to put something coherent.

<>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 59f6268..6e8f3f6 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -1982,6 +1982,19 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page,
>>  	return ret;
>>  }
>>  
>> +static int do_pfn_mkwrite(struct vm_area_struct *vma, unsigned long address)
>> +{
>> +	struct vm_fault vmf = {
>> +		.page = 0,
> 
> .page = NULL,
> 
>> +		.pgoff = (((address & PAGE_MASK) - vma->vm_start)
>> +					>> PAGE_SHIFT) + vma->vm_pgoff,
> 
> .pgoff = linear_page_index(vma, address),
> 

Yes I had fixes for these two

>> +		.virtual_address = (void __user *)(address & PAGE_MASK),
>> +		.flags = FAULT_FLAG_WRITE | FAULT_FLAG_MKWRITE,
>> +	};
>> +
>> +	return vma->vm_ops->pfn_mkwrite(vma, &vmf);
>> +}
>> +
>>  /*
>>   * Handle write page faults for pages that can be reused in the current vma
>>   *
>> @@ -2259,14 +2272,28 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
>>  		 * VM_PFNMAP VMA.
>>  		 *
>>  		 * We should not cow pages in a shared writeable mapping.
>> -		 * Just mark the pages writable as we can't do any dirty
>> -		 * accounting on raw pfn maps.
>> +		 * Just mark the pages writable and/or call ops->pfn_mkwrite.
>>  		 */
>>  		if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
>> -				     (VM_WRITE|VM_SHARED))
>> +				     (VM_WRITE|VM_SHARED)) {
> 
> Let's move this case in separate function -- wp_pfn_shared(). As we do for
> wp_page_shared().
> 

Ha, OK I will try that. I will need to re-run tests to make sure I did
not mess up

Thanks will fix, makes sense
Boaz

>> +			if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
>> +				int ret;
>> +
>> +				pte_unmap_unlock(page_table, ptl);
>> +				ret = do_pfn_mkwrite(vma, address);
>> +				if (ret & VM_FAULT_ERROR)
>> +					return ret;
>> +				page_table = pte_offset_map_lock(mm, pmd,
>> +								 address, &ptl);
>> +				/* Did pfn_mkwrite already fixed up the pte */
>> +				if (!pte_same(*page_table, orig_pte)) {
>> +					pte_unmap_unlock(page_table, ptl);
>> +					return ret;
>> +				}
>> +			}
>>  			return wp_page_reuse(mm, vma, address, page_table, ptl,
>>  					     orig_pte, old_page, 0, 0);
>> -
>> +		}
>>  		pte_unmap_unlock(page_table, ptl);
>>  		return wp_page_copy(mm, vma, address, page_table, pmd,
>>  				    orig_pte, old_page);

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