Re: [Ocfs2-devel] [PATCH v2 05/10] fsdax: Replace mmap entry in case of CoW

[Christoph Hellwig <hch@lst.de>]

On Fri, Feb 26, 2021 at 08:20:25AM +0800, Shiyang Ruan wrote:
> We replace the existing entry to the newly allocated one in case of CoW.
> Also, we mark the entry as PAGECACHE_TAG_TOWRITE so writeback marks this
> entry as writeprotected.  This helps us snapshots so new write
> pagefaults after snapshots trigger a CoW.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> ---
>  fs/dax.c | 37 ++++++++++++++++++++++++++-----------
>  1 file changed, 26 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 748dfb89fb41..ec4b733e0b59 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -722,6 +722,9 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
>  	return 0;
>  }
>  
> +#define DAX_IF_DIRTY		(1 << 0)
> +#define DAX_IF_COW		(1 << 1)
> +
>  /*
>   * By this point grab_mapping_entry() has ensured that we have a locked entry
>   * of the appropriate size so we don't have to worry about downgrading PMDs to
> @@ -729,16 +732,19 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
>   * already in the tree, we will skip the insertion and just dirty the PMD as
>   * appropriate.
>   */
> -static void *dax_insert_entry(struct xa_state *xas,
> -		struct address_space *mapping, struct vm_fault *vmf,
> -		void *entry, pfn_t pfn, unsigned long flags, bool dirty)
> +static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> +		void *entry, pfn_t pfn, unsigned long flags,
> +		unsigned int insert_flags)
>  {
> +	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
>  	void *new_entry = dax_make_entry(pfn, flags);
> +	bool dirty = insert_flags & DAX_IF_DIRTY;
> +	bool cow = insert_flags & DAX_IF_COW;
>  
>  	if (dirty)
>  		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

I still think the __mark_inode_dirty should just be moved into the one
caller that needs it.

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