From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
Date: Tue, 19 Jun 2012 13:46:48 +0000
Subject: Re: [PATCH 3/4] KVM: MMU: Make kvm_handle_hva() handle range of addresses
Message-Id: <20120619224648.bbb360c6eeae9887de7b1f93@gmail.com>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20120615203007.4f61bb17.yoshikawa.takuya@oss.ntt.co.jp>
	<20120615203230.2c577652.yoshikawa.takuya@oss.ntt.co.jp>
	<4FDF1AFE.4000607@redhat.com>
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To: Avi Kivity <avi@redhat.com>
Cc: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>, mtosatti@redhat.com, agraf@suse.de, paulus@samba.org, aarcange@redhat.com, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org

On Mon, 18 Jun 2012 15:11:42 +0300
Avi Kivity <avi@redhat.com> wrote:

> Potential for improvement: don't do 512 iterations on same large page.
> 
> Something like
> 
>     if ((gfn ^ prev_gfn) & mask(level))
>         ret |= handler(...)
> 
> with clever selection of the first prev_gfn so it always matches (~gfn
> maybe).


I thought up a better solution:

1. Separate rmap_pde from lpage_info->write_count and
   make this a simple array. (I once tried this.)

2. Use gfn_to_index() and loop over rmap array:
 ...
  /* intersection check */
  start = max(start, memslot->userspace_addr);
  end = min(end, memslot->userspace_addr +
                 (memslot->npages << PAGE_SHIFT));
  if (start > end)
      continue;

  /* hva to gfn conversion */
  gfn_start = hva_to_gfn_memslot(start);
  gfn_end = hva_to_gfn_memslot(end);

  /* main part */
  for each level {
      rmapp = __gfn_to_rmap(gfn_start, level, memslot);
      for (idx = gfn_to_index(gfn_start, memslot->base_gfn, level);
           idx < gfn_to_index(gfn_end, memslot->base_gfn, level); idx++) {
              ...
          /* loop over rmap array */
          ret |= handler(kvm, rmapp + idx, data);
      }
  }


Thanks,
	Takuya