Re: [PATCH v3] btrfs: refactor alloc_extent_buffer() to allocate-then-attach method

[Josef Bacik <josef@toxicpanda.com>]

On Fri, Nov 24, 2023 at 06:14:16PM +1030, Qu Wenruo wrote:
> Currently alloc_extent_buffer() utilizes find_or_create_page() to
> allocate one page a time for an extent buffer.
> 
> This method has the following disadvantages:
> 
> - find_or_create_page() is the legacy way of allocating new pages
>   With the new folio infrastructure, find_or_create_page() is just
>   redirected to filemap_get_folio().
> 
> - Lacks the way to support higher order (order >= 1) folios
>   As we can not yet let filemap to give us a higher order folio (yet).
> 
> This patch would change the workflow by the following way:
> 
> 		Old		   |		new
> -----------------------------------+-------------------------------------
>                                    | ret = btrfs_alloc_page_array();
> for (i = 0; i < num_pages; i++) {  | for (i = 0; i < num_pages; i++) {
>     p = find_or_create_page();     |     ret = filemap_add_folio();
>     /* Attach page private */      |     /* Reuse page cache if needed */
>     /* Reused eb if needed */      |
> 				   |     /* Attach page private and
> 				   |        reuse eb if needed */
> 				   | }
> 
> By this we split the page allocation and private attaching into two
> parts, allowing future updates to each part more easily, and migrate to
> folio interfaces (especially for possible higher order folios).
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Sorry I just noticed the updated version of this, I sent my comments in reply to
an older version but they still hold true for this version.  Thanks,

Josef