linux-kernel - Re: [PATCH 14/16] block: use memcpy_from_bvec in __blk_queue

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Message-ID: <20210609015819.GU3697498@iweiny-DESK2.sc.intel.com>
Date:   Tue, 8 Jun 2021 18:58:19 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geoff Levand <geoff@...radead.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ceph-devel@...r.kernel.org
Subject: Re: [PATCH 14/16] block: use memcpy_from_bvec in __blk_queue_bounce

On Tue, Jun 08, 2021 at 06:06:01PM +0200, Christoph Hellwig wrote:
> Rewrite the actual bounce buffering loop in __blk_queue_bounce to that
> the memcpy_to_bvec helper can be used to perform the data copies.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  block/bounce.c | 21 +++++++--------------
>  1 file changed, 7 insertions(+), 14 deletions(-)
> 
> diff --git a/block/bounce.c b/block/bounce.c
> index a2fc6326b6c9..b5ad09e07bcf 100644
> --- a/block/bounce.c
> +++ b/block/bounce.c
> @@ -243,24 +243,17 @@ void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
>  	 * because the 'bio' is single-page bvec.
>  	 */
>  	for (i = 0, to = bio->bi_io_vec; i < bio->bi_vcnt; to++, i++) {
> -		struct page *page = to->bv_page;
> +		struct page *bounce_page;
>  
> -		if (!PageHighMem(page))
> +		if (!PageHighMem(to->bv_page))
>  			continue;
>  
> -		to->bv_page = mempool_alloc(&page_pool, GFP_NOIO);
> -		inc_zone_page_state(to->bv_page, NR_BOUNCE);
> +		bounce_page = mempool_alloc(&page_pool, GFP_NOIO);
> +		inc_zone_page_state(bounce_page, NR_BOUNCE);
>  
> -		if (rw == WRITE) {
> -			char *vto, *vfrom;
> -
> -			flush_dcache_page(page);
> -
> -			vto = page_address(to->bv_page) + to->bv_offset;
> -			vfrom = kmap_atomic(page) + to->bv_offset;
> -			memcpy(vto, vfrom, to->bv_len);
> -			kunmap_atomic(vfrom);
> -		}
> +		if (rw == WRITE)
> +			memcpy_from_bvec(page_address(bounce_page), to);

NIT: the fact that the copy is from 'to' makes my head hurt...  But I don't
see a good way to change that without declaring unnecessary variables...  :-(

The logic seems right.

Ira

> +		to->bv_page = bounce_page;
>  	}
>  
>  	trace_block_bio_bounce(*bio_orig);
> -- 
> 2.30.2
>