Re: [PATCH v5 04/18] btrfs: make attach_extent_buffer_page() handle subpage case

[Josef Bacik <josef@toxicpanda.com>]

On 1/26/21 3:33 AM, Qu Wenruo wrote:
> For subpage case, we need to allocate additional memory for each
> metadata page.
> 
> So we need to:
> 
> - Allow attach_extent_buffer_page() to return int to indicate allocation
>    failure
> 
> - Allow manually pre-allocate subpage memory for alloc_extent_buffer()
>    As we don't want to use GFP_ATOMIC under spinlock, we introduce
>    btrfs_alloc_subpage() and btrfs_free_subpage() functions for this
>    purpose.
>    (The simple wrap for btrfs_free_subpage() is for later convert to
>     kmem_cache. Already internally tested without problem)
> 
> - Preallocate btrfs_subpage structure for alloc_extent_buffer()
>    We don't want to call memory allocation with spinlock held, so
>    do preallocation before we acquire mapping->private_lock.
> 
> - Handle subpage and regular case differently in
>    attach_extent_buffer_page()
>    For regular case, no change, just do the usual thing.
>    For subpage case, allocate new memory or use the preallocated memory.
> 
> For future subpage metadata, we will make use of radix tree to grab
> extent buffer.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> Reviewed-by: David Sterba <dsterba@suse.com>
> Signed-off-by: David Sterba <dsterba@suse.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef