Re: [PATCH 03/26] netfs: Update i_blocks when write committed to pagecache

[Jeff Layton]

On Thu, 2024-03-28 at 16:33 +0000, David Howells wrote:
> Update i_blocks when i_size is updated when we finish making a write to the
> pagecache to reflect the amount of space we think will be consumed.
> 

Umm ok, but why? I get that the i_size and i_blocks would be out of sync
until we get back new attrs from the server, but is that a problem? I'm
mainly curious as to what's paying attention to the i_blocks during this
window.

> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Steve French <sfrench@xxxxxxxxx>
> cc: Shyam Prasad N <nspmangalore@xxxxxxxxx>
> cc: Rohith Surabattula <rohiths.msft@xxxxxxxxx>
> cc: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: linux-cifs@xxxxxxxxxxxxxxx
> cc: netfs@xxxxxxxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> cc: linux-mm@xxxxxxxxx
> ---
>  fs/netfs/buffered_write.c | 45 +++++++++++++++++++++++++++++----------
>  1 file changed, 34 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
> index 9a0d32e4b422..c194655a6dcf 100644
> --- a/fs/netfs/buffered_write.c
> +++ b/fs/netfs/buffered_write.c
> @@ -130,6 +130,37 @@ static struct folio *netfs_grab_folio_for_write(struct address_space *mapping,
>  				   mapping_gfp_mask(mapping));
>  }
>  
> +/*
> + * Update i_size and estimate the update to i_blocks to reflect the additional
> + * data written into the pagecache until we can find out from the server what
> + * the values actually are.
> + */
> +static void netfs_update_i_size(struct netfs_inode *ctx, struct inode *inode,
> +				loff_t i_size, loff_t pos, size_t copied)
> +{
> +	blkcnt_t add;
> +	size_t gap;
> +
> +	if (ctx->ops->update_i_size) {
> +		ctx->ops->update_i_size(inode, pos);
> +		return;
> +	}
> +
> +	i_size_write(inode, pos);
> +#if IS_ENABLED(CONFIG_FSCACHE)
> +	fscache_update_cookie(ctx->cache, NULL, &pos);
> +#endif
> +
> +	gap = SECTOR_SIZE - (i_size & (SECTOR_SIZE - 1));
> +	if (copied > gap) {
> +		add = DIV_ROUND_UP(copied - gap, SECTOR_SIZE);
> +
> +		inode->i_blocks = min_t(blkcnt_t,
> +					DIV_ROUND_UP(pos, SECTOR_SIZE),
> +					inode->i_blocks + add);
> +	}
> +}
> +
>  /**
>   * netfs_perform_write - Copy data into the pagecache.
>   * @iocb: The operation parameters
> @@ -352,18 +383,10 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
>  		trace_netfs_folio(folio, trace);
>  
>  		/* Update the inode size if we moved the EOF marker */
> -		i_size = i_size_read(inode);
>  		pos += copied;
> -		if (pos > i_size) {
> -			if (ctx->ops->update_i_size) {
> -				ctx->ops->update_i_size(inode, pos);
> -			} else {
> -				i_size_write(inode, pos);
> -#if IS_ENABLED(CONFIG_FSCACHE)
> -				fscache_update_cookie(ctx->cache, NULL, &pos);
> -#endif
> -			}
> -		}
> +		i_size = i_size_read(inode);
> +		if (pos > i_size)
> +			netfs_update_i_size(ctx, inode, i_size, pos, copied);
>  		written += copied;
>  
>  		if (likely(!wreq)) {
> 

Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>