Re: [PATCH] bcache: back to cache all readahead I/Os

[Eric Wheeler <bcache@lists.ewheeler.net>]

On Sat, 4 Jan 2020, Coly Li wrote:

> In year 2007 high performance SSD was still expensive, in order to
> save more space for real workload or meta data, the readahead I/Os
> for non-meta data was bypassed and not cached on SSD.
> 
> In now days, SSD price drops a lot and people can find larger size
> SSD with more comfortable price. It is unncessary to bypass normal
> readahead I/Os to save SSD space for now.
> 
> This patch removes the code which checks REQ_RAHEAD tag of bio in
> check_should_bypass(), then all readahead I/Os will be cached on SSD.
> 
> NOTE: this patch still keeps the checking of "REQ_META|REQ_PRIO" in
> should_writeback(), because we still want to cache meta data I/Os
> even they are asynchronized.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Coly Li <colyli@suse.de>
> Cc: Eric Wheeler <bcache@linux.ewheeler.net>

Acked-by: Eric Wheeler <bcache@linux.ewheeler.net>


> ---
>  drivers/md/bcache/request.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 73478a91a342..acc07c4f27ae 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -378,15 +378,6 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
>  	     op_is_write(bio_op(bio))))
>  		goto skip;
>  
> -	/*
> -	 * Flag for bypass if the IO is for read-ahead or background,
> -	 * unless the read-ahead request is for metadata
> -	 * (eg, for gfs2 or xfs).
> -	 */
> -	if (bio->bi_opf & (REQ_RAHEAD|REQ_BACKGROUND) &&
> -	    !(bio->bi_opf & (REQ_META|REQ_PRIO)))
> -		goto skip;
> -
>  	if (bio->bi_iter.bi_sector & (c->sb.block_size - 1) ||
>  	    bio_sectors(bio) & (c->sb.block_size - 1)) {
>  		pr_debug("skipping unaligned io");
> -- 
> 2.16.4
> 
>