linux-kernel - Re: [PATCH 2/4] fs/buffer: avoid redundant lookup in getblk slowpath

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Message-ID: <hjjkstrkljfsx2jxhlgif4jsox6lsaute6tx4bhk3yufxqs5re@qo3zuncbozph>
Date: Fri, 16 May 2025 12:12:59 +0200
From: Jan Kara <jack@...e.cz>
To: Davidlohr Bueso <dave@...olabs.net>
Cc: brauner@...nel.org, jack@...e.cz, viro@...iv.linux.org.uk, 
	mcgrof@...nel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] fs/buffer: avoid redundant lookup in getblk slowpath

On Thu 15-05-25 10:39:23, Davidlohr Bueso wrote:
> __getblk_slow() already implies failing a first lookup
> as the fastpath, so try to create the buffers immediately
> and avoid the redundant lookup. This saves 5-10% of the
> total cost/latency of the slowpath.
> 
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>

Makes sense. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/buffer.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 5a4342881f3b..b02cced96529 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1139,15 +1139,15 @@ __getblk_slow(struct block_device *bdev, sector_t block,
>  	for (;;) {
>  		struct buffer_head *bh;
>  
> +		if (!grow_buffers(bdev, block, size, gfp))
> +			return NULL;
> +
>  		if (blocking)
>  			bh = __find_get_block_nonatomic(bdev, block, size);
>  		else
>  			bh = __find_get_block(bdev, block, size);
>  		if (bh)
>  			return bh;
> -
> -		if (!grow_buffers(bdev, block, size, gfp))
> -			return NULL;
>  	}
>  }
>  
> -- 
> 2.39.5
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR