linux-kernel - Re: [PATCH 2/4] KVM: Avoid checking huge page mappings in get_dirty

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Message-Id: <20120302115624.46cbaa00.yoshikawa.takuya@oss.ntt.co.jp>
Date:	Fri, 2 Mar 2012 11:56:24 +0900
From:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
To:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
Cc:	avi@...hat.com, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] KVM: Avoid checking huge page mappings in
 get_dirty_log()

Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp> wrote:

> +	while (mask) {
> +		rmapp = &slot->rmap[gfn_offset + __ffs(mask)];
> +		__rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);
>  
> -	return write_protected;
> +		/* clear the first set bit */
> +		mask &= mask - 1;
> +	}
>  }

while (mask) {
	fsbit = __ffs(mask);
	gfn_offset += fsbit;
	mask >>= fsbit + 1;

	rmapp = &slot->rmap[gfn_offset];
	__rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);
}

Seems to be better: BSF friendly.

I will update this function and post the result with dirty-log-perf output!

	Takuya
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