Re: [PATCH 07/10] bcache: use bvec_kmap_local in bio_csum

From: Ira Weiny <ira.weiny@intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	Justin Sanders <justin@coraid.com>,
	Philipp Reisner <philipp.reisner@linbit.com>,
	Lars Ellenberg <lars.ellenberg@linbit.com>,
	Denis Efremov <efremov@linux.com>,
	Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>,
	Coly Li <colyli@suse.de>, Dan Williams <dan.j.williams@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	linux-xtensa@linux-xtensa.org, linux-block@vger.kernel.org,
	drbd-dev@lists.linbit.com, linux-bcache@vger.kernel.org,
	nvdimm@lists.linux.dev
Subject: Re: [PATCH 07/10] bcache: use bvec_kmap_local in bio_csum
Date: Mon, 28 Feb 2022 20:00:01 -0800	[thread overview]
Message-ID: <Yh2aQROdfk1iUuQV@iweiny-desk3> (raw)
In-Reply-To: <20220222155156.597597-8-hch@lst.de>

On Tue, Feb 22, 2022 at 04:51:53PM +0100, Christoph Hellwig wrote:
> Using local kmaps slightly reduces the chances to stray writes, and
> the bvec interface cleans up the code a little bit.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/md/bcache/request.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 6869e010475a3..4e55ca8ca67ff 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -44,10 +44,10 @@ static void bio_csum(struct bio *bio, struct bkey *k)
>  	uint64_t csum = 0;
>  
>  	bio_for_each_segment(bv, bio, iter) {
> -		void *d = kmap(bv.bv_page) + bv.bv_offset;
> +		void *d = bvec_kmap_local(&bv);
>  
>  		csum = crc64_be(csum, d, bv.bv_len);
> -		kunmap(bv.bv_page);
> +		kunmap(d);

kunmap_local()

Ira

>  	}
>  
>  	k->ptr[KEY_PTRS(k)] = csum & (~0ULL >> 1);
> -- 
> 2.30.2
> 
>