linux-kernel - Re: [PATCH 1/6] block: Introduce bio_for_each

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Date:	Wed, 25 Sep 2013 14:17:02 -0700
From:	Zach Brown <zab@...hat.com>
To:	Kent Overstreet <kmo@...erainc.com>
Cc:	hch@...radead.org, axboe@...nel.dk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] block: Introduce bio_for_each_page()

>  void zero_fill_bio(struct bio *bio)
>  {
> -	unsigned long flags;
>  	struct bio_vec bv;
>  	struct bvec_iter iter;
>  
> -	bio_for_each_segment(bv, bio, iter) {
> +#if defined(CONFIG_HIGHMEM) || defined(ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE)
> +	bio_for_each_page(bv, bio, iter) {
> +		unsigned long flags;
>  		char *data = bvec_kmap_irq(&bv, &flags);
>  		memset(data, 0, bv.bv_len);
>  		flush_dcache_page(bv.bv_page);
>  		bvec_kunmap_irq(data, &flags);
>  	}
> +#else
> +	bio_for_each_segment(bv, bio, iter)
> +		memset(page_address(bv.bv_page) + bv.bv_offset,
> +		       0, bv.bv_len);
> +#endif

This looks pretty sketchy.  I'd expect this to be doable with one loop
and that bvec_kmap_irq() and flush_dcache_page() would fall back to
page_address() and nops when they're not needed.

Where did this come from?

- z
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