linux-ext4 - Re: [PATCH v2 6/8] fs/ext4: use sleeping version of __find_get

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Message-ID: <g2xj2du3t226jve57mw4wiig4zpqqsvomtbzeu4wk37dfqbp47@3l66fjg736yy>
Date: Thu, 10 Apr 2025 15:36:25 +0200
From: Jan Kara <jack@...e.cz>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: brauner@...nel.org, jack@...e.cz, tytso@....edu, 
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, riel@...riel.com, dave@...olabs.net, 
	willy@...radead.org, hannes@...xchg.org, oliver.sang@...el.com, david@...hat.com, 
	axboe@...nel.dk, hare@...e.de, david@...morbit.com, djwong@...nel.org, 
	ritesh.list@...il.com, linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org, 
	linux-mm@...ck.org, gost.dev@...sung.com, p.raghav@...sung.com, da.gomez@...sung.com
Subject: Re: [PATCH v2 6/8] fs/ext4: use sleeping version of
 __find_get_block()

On Wed 09-04-25 18:49:43, Luis Chamberlain wrote:
> From: Davidlohr Bueso <dave@...olabs.net>
> 
> Trivially introduce the wrapper and enable ext4_free_blocks() to use
> it, which has a cond_resched to begin with. Convert to the new nonatomic
> flavor to benefit from potential performance benefits and adapt in the
> future vs migration such that semantics are kept.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  fs/ext4/inode.c             | 2 ++
>  fs/ext4/mballoc.c           | 3 ++-
>  include/linux/buffer_head.h | 6 ++++++
>  3 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 1dc09ed5d403..b7acb5d3adcb 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -860,6 +860,8 @@ struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
>  		return sb_find_get_block(inode->i_sb, map.m_pblk);
>  
>  	/*
> +	 * Potential TODO: use sb_find_get_block_nonatomic() instead.
> +	 *

Yes, please. Since we are behind nowait check, we are fine with blocking...

								Honza

>  	 * Since bh could introduce extra ref count such as referred by
>  	 * journal_head etc. Try to avoid using __GFP_MOVABLE here
>  	 * as it may fail the migration when journal_head remains.
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 0d523e9fb3d5..6f4265b21e19 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -6644,7 +6644,8 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
>  		for (i = 0; i < count; i++) {
>  			cond_resched();
>  			if (is_metadata)
> -				bh = sb_find_get_block(inode->i_sb, block + i);
> +				bh = sb_find_get_block_nonatomic(inode->i_sb,
> +								 block + i);
>  			ext4_forget(handle, is_metadata, inode, bh, block + i);
>  		}
>  	}
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index 2b5458517def..8db10ca288fc 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -399,6 +399,12 @@ sb_find_get_block(struct super_block *sb, sector_t block)
>  	return __find_get_block(sb->s_bdev, block, sb->s_blocksize);
>  }
>  
> +static inline struct buffer_head *
> +sb_find_get_block_nonatomic(struct super_block *sb, sector_t block)
> +{
> +	return __find_get_block_nonatomic(sb->s_bdev, block, sb->s_blocksize);
> +}
> +

This hunk probably belongs to some introductory patch implementing
nonatomic helpers.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR