Re: [PATCH 1/2] btrfs: additional gfp api for allocating compressed folios

[Mark Harmstone <mark@harmstone.com>]

Reviewed-by: Mark Harmstone <mark@harmstone.com>

On 20/03/2026 7.34 am, JP Kobryn (Meta) wrote:
> btrfs_alloc_compr_folio() assumes all callers want GFP_NOFS. This is fine
> for most cases, however there are some call sites that would benefit from
> different flags. One such case is preventing direct reclaim from occurring
> during readahead allocations. With unbounded reclaim during this time,
> noticeable latency will occur under high memory pressure.
> 
> Provide an additional API that accepts one additional gfp_t parameter,
> giving callers flexibility over the characteristics of their allocation.
> 
> Signed-off-by: JP Kobryn (Meta) <jp.kobryn@linux.dev>
> ---
>   fs/btrfs/compression.c | 9 +++++++--
>   fs/btrfs/compression.h | 1 +
>   2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index 192f133d9eb5..ae9cb5b7676c 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -180,7 +180,7 @@ static unsigned long btrfs_compr_pool_scan(struct shrinker *sh, struct shrink_co
>   /*
>    * Common wrappers for page allocation from compression wrappers
>    */
> -struct folio *btrfs_alloc_compr_folio(struct btrfs_fs_info *fs_info)
> +struct folio *btrfs_alloc_compr_folio_gfp(struct btrfs_fs_info *fs_info, gfp_t gfp)
>   {
>   	struct folio *folio = NULL;
>   
> @@ -200,7 +200,12 @@ struct folio *btrfs_alloc_compr_folio(struct btrfs_fs_info *fs_info)
>   		return folio;
>   
>   alloc:
> -	return folio_alloc(GFP_NOFS, fs_info->block_min_order);
> +	return folio_alloc(gfp, fs_info->block_min_order);
> +}
> +
> +struct folio *btrfs_alloc_compr_folio(struct btrfs_fs_info *fs_info)
> +{
> +	return btrfs_alloc_compr_folio_gfp(fs_info, GFP_NOFS);
>   }
>   
>   void btrfs_free_compr_folio(struct folio *folio)
> diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
> index 973530e9ce6c..6131c128dd21 100644
> --- a/fs/btrfs/compression.h
> +++ b/fs/btrfs/compression.h
> @@ -99,6 +99,7 @@ void btrfs_submit_compressed_read(struct btrfs_bio *bbio);
>   int btrfs_compress_str2level(unsigned int type, const char *str, int *level_ret);
>   
>   struct folio *btrfs_alloc_compr_folio(struct btrfs_fs_info *fs_info);
> +struct folio *btrfs_alloc_compr_folio_gfp(struct btrfs_fs_info *fs_info, gfp_t gfp);
>   void btrfs_free_compr_folio(struct folio *folio);
>   
>   struct workspace_manager {