linux-kernel - Re: [PATCH V10 15/19] block: always define BIO_MAX

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Date:   Thu, 15 Nov 2018 17:59:36 -0800
From:   Omar Sandoval <osandov@...ndov.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dave Chinner <dchinner@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>,
        Christoph Hellwig <hch@....de>, Theodore Ts'o <tytso@....edu>,
        linux-ext4@...r.kernel.org, Coly Li <colyli@...e.de>,
        linux-bcache@...r.kernel.org, Boaz Harrosh <ooo@...ctrozaur.com>,
        Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com
Subject: Re: [PATCH V10 15/19] block: always define BIO_MAX_PAGES as 256

On Thu, Nov 15, 2018 at 04:53:02PM +0800, Ming Lei wrote:
> Now multi-page bvec can cover CONFIG_THP_SWAP, so we don't need to
> increase BIO_MAX_PAGES for it.

You mentioned to it in the cover letter, but this needs more explanation
in the commit message. Why did CONFIG_THP_SWAP require > 256? Why does
multipage bvecs remove that requirement?

> Cc: Dave Chinner <dchinner@...hat.com>
> Cc: Kent Overstreet <kent.overstreet@...il.com>
> Cc: Mike Snitzer <snitzer@...hat.com>
> Cc: dm-devel@...hat.com
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: Shaohua Li <shli@...nel.org>
> Cc: linux-raid@...r.kernel.org
> Cc: linux-erofs@...ts.ozlabs.org
> Cc: David Sterba <dsterba@...e.com>
> Cc: linux-btrfs@...r.kernel.org
> Cc: Darrick J. Wong <darrick.wong@...cle.com>
> Cc: linux-xfs@...r.kernel.org
> Cc: Gao Xiang <gaoxiang25@...wei.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Theodore Ts'o <tytso@....edu>
> Cc: linux-ext4@...r.kernel.org
> Cc: Coly Li <colyli@...e.de>
> Cc: linux-bcache@...r.kernel.org
> Cc: Boaz Harrosh <ooo@...ctrozaur.com>
> Cc: Bob Peterson <rpeterso@...hat.com>
> Cc: cluster-devel@...hat.com
> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---
>  include/linux/bio.h | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 5040e9a2eb09..277921ad42e7 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -34,15 +34,7 @@
>  #define BIO_BUG_ON
>  #endif
>  
> -#ifdef CONFIG_THP_SWAP
> -#if HPAGE_PMD_NR > 256
> -#define BIO_MAX_PAGES		HPAGE_PMD_NR
> -#else
>  #define BIO_MAX_PAGES		256
> -#endif
> -#else
> -#define BIO_MAX_PAGES		256
> -#endif
>  
>  #define bio_prio(bio)			(bio)->bi_ioprio
>  #define bio_set_prio(bio, prio)		((bio)->bi_ioprio = prio)
> -- 
> 2.9.5
>