linux-kernel - Re: [PATCH] blk: improve order of bio handling in generic_make

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Message-ID: <87lgsjj9w8.fsf@notabene.neil.brown.name>
Date:   Mon, 06 Mar 2017 15:40:07 +1100
From:   NeilBrown <neilb@...e.com>
To:     Jack Wang <jinpu.wang@...fitbricks.com>,
        Jens Axboe <axboe@...nel.dk>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Pavel Machek <pavel@....cz>, Mike Snitzer <snitzer@...hat.com>,
        Mikulas Patocka <mpatocka@...hat.com>
Subject: Re: [PATCH] blk: improve order of bio handling in generic_make_request()

On Fri, Mar 03 2017, Jack Wang wrote:
>
> Thanks Neil for pushing the fix.
>
> We can optimize generic_make_request a little bit:
> - assign bio_list struct hold directly instead init and merge
> - remove duplicate code
>
> I think better to squash into your fix.

Hi Jack,
 I don't object to your changes, but I'd like to see a response from
 Jens first.
 My preference would be to get the original patch in, then other changes
 that build on it, such as this one, can be added.  Until the core
 changes lands, any other work is pointless.

 Of course if Jens wants a this merged before he'll apply it, I'll
 happily do that.

Thanks,
NeilBrown



> ---
>  block/blk-core.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 3bc7202..b29b7e5 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -2147,8 +2147,7 @@ blk_qc_t generic_make_request(struct bio *bio)
>  			struct bio_list lower, same, hold;
>  
>  			/* Create a fresh bio_list for all subordinate requests */
> -			bio_list_init(&hold);
> -			bio_list_merge(&hold, &bio_list_on_stack);
> +			hold = bio_list_on_stack;
>  			bio_list_init(&bio_list_on_stack);
>  
>  			ret = q->make_request_fn(q, bio);
> @@ -2168,14 +2167,10 @@ blk_qc_t generic_make_request(struct bio *bio)
>  			bio_list_merge(&bio_list_on_stack, &lower);
>  			bio_list_merge(&bio_list_on_stack, &same);
>  			bio_list_merge(&bio_list_on_stack, &hold);
> -
> -			bio = bio_list_pop(current->bio_list);
>  		} else {
> -			struct bio *bio_next = bio_list_pop(current->bio_list);
> -
>  			bio_io_error(bio);
> -			bio = bio_next;
>  		}
> +		bio = bio_list_pop(current->bio_list);
>  	} while (bio);
>  	current->bio_list = NULL; /* deactivate */
>  
> -- 
>
> Regards,
> Jack 

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