Date: Wed, 25 Sep 2013 14:17:02 -0700
From: Zach Brown <zab@redhat.com>
To: Kent Overstreet <kmo@daterainc.com>
Cc: hch@infradead.org, axboe@kernel.dk, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] block: Introduce bio_for_each_page()
Message-ID: <20130925211702.GH30372@lenny.home.zabbo.net>
References: <1380140564-9030-1-git-send-email-kmo@daterainc.com>
 <1380140564-9030-2-git-send-email-kmo@daterainc.com>
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>  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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