Re: [PATCH 05/11] filesystem-dax: set page->index

[Jan Kara <jack@suse.cz>]

On Tue 22-05-18 07:39:57, Dan Williams wrote:
> In support of enabling memory_failure() handling for filesystem-dax
> mappings, set ->index to the pgoff of the page. The rmap implementation
> requires ->index to bound the search through the vma interval tree. The
> index is set and cleared at dax_associate_entry() and
> dax_disassociate_entry() time respectively.
> 
> Cc: Jan Kara <jack@suse.cz>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Matthew Wilcox <mawilcox@microsoft.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  fs/dax.c |   11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index aaec72ded1b6..2e4682cd7c69 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -319,18 +319,22 @@ static unsigned long dax_radix_end_pfn(void *entry)
>  	for (pfn = dax_radix_pfn(entry); \
>  			pfn < dax_radix_end_pfn(entry); pfn++)
>  
> -static void dax_associate_entry(void *entry, struct address_space *mapping)
> +static void dax_associate_entry(void *entry, struct address_space *mapping,
> +		struct vm_area_struct *vma, unsigned long address)
>  {
> -	unsigned long pfn;
> +	unsigned long size = dax_entry_size(entry), pfn, index;
> +	int i = 0;
>  
>  	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
>  		return;
>  
> +	index = linear_page_index(vma, address & ~(size - 1));
>  	for_each_mapped_pfn(entry, pfn) {
>  		struct page *page = pfn_to_page(pfn);
>  
>  		WARN_ON_ONCE(page->mapping);
>  		page->mapping = mapping;
> +		page->index = index + i++;
>  	}
>  }

Hum, this just made me think: How is this going to work with XFS reflink?
In fact is not the page->mapping association already broken by XFS reflink?
Because with reflink we can have two or more mappings pointing to the same
physical blocks (i.e., pages in DAX case)...

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR