linux-kernel - Re: [RFC PATCH V6 3/7] ovl: implement overlayfs' own ->write

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Date:   Fri, 26 Nov 2021 10:14:30 +0100
From:   Jan Kara <jack@...e.cz>
To:     Chengguang Xu <cgxu519@...ernel.net>
Cc:     miklos@...redi.hu, jack@...e.cz, amir73il@...il.com,
        linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chengguang Xu <charliecgxu@...cent.com>
Subject: Re: [RFC PATCH V6 3/7] ovl: implement overlayfs' own ->write_inode
 operation

On Mon 22-11-21 11:00:34, Chengguang Xu wrote:
> From: Chengguang Xu <charliecgxu@...cent.com>
> 
> Sync dirty data and meta of upper inode in overlayfs' ->write_inode()
> and redirty overlayfs' inode.
> 
> Signed-off-by: Chengguang Xu <charliecgxu@...cent.com>

Looks good. I'm still not 100% convinced keeping inodes dirty all the time
will not fire back in excessive writeback activity (e.g. flush worker will
traverse the list of all dirty inodes every 30 seconds and try to write
them) but I guess we can start with this and if people complain, dirtiness
handling can be improved. So feel free to add:

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

								Honza

> ---
>  fs/overlayfs/super.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 18a12088a37b..12acf0ec7395 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -15,6 +15,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/posix_acl_xattr.h>
>  #include <linux/exportfs.h>
> +#include <linux/writeback.h>
>  #include "overlayfs.h"
>  
>  MODULE_AUTHOR("Miklos Szeredi <miklos@...redi.hu>");
> @@ -406,12 +407,32 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
>  	return ret;
>  }
>  
> +static int ovl_write_inode(struct inode *inode,
> +			   struct writeback_control *wbc)
> +{
> +	struct ovl_fs *ofs = inode->i_sb->s_fs_info;
> +	struct inode *upper_inode = ovl_inode_upper(inode);
> +	int ret = 0;
> +
> +	if (!upper_inode)
> +		return 0;
> +
> +	if (!ovl_should_sync(ofs))
> +		return 0;
> +
> +	ret = write_inode_now(upper_inode, wbc->sync_mode == WB_SYNC_ALL);
> +	mark_inode_dirty(inode);
> +
> +	return ret;
> +}
> +
>  static const struct super_operations ovl_super_operations = {
>  	.alloc_inode	= ovl_alloc_inode,
>  	.free_inode	= ovl_free_inode,
>  	.destroy_inode	= ovl_destroy_inode,
>  	.drop_inode	= generic_delete_inode,
>  	.put_super	= ovl_put_super,
> +	.write_inode	= ovl_write_inode,
>  	.sync_fs	= ovl_sync_fs,
>  	.statfs		= ovl_statfs,
>  	.show_options	= ovl_show_options,
> -- 
> 2.27.0
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR