linux-kernel - Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte and mmu notifier to help KSM dirty bit tracking

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Date:	Thu, 23 Jun 2011 01:44:50 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Nai Xia <nai.xia@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	Hugh Dickins <hughd@...gle.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Rik van Riel <riel@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte
 and mmu notifier to help KSM dirty bit tracking

On Thu, Jun 23, 2011 at 07:19:06AM +0800, Nai Xia wrote:
> OK, I'll have a try over other workarounds.
> I am not feeling good about need_pte_unmap myself. :-)

The usual way is to check VM_HUGETLB in the caller and to call another
function that doesn't kmap. Casting pmd_t to pte_t isn't really nice
(but hey we're also doing that exceptionally in smaps_pte_range for
THP, but it safe there because we're casting the value of the pmd, not
the pointer to the pmd, so the kmap is done by the pte version of the
caller and not done by the pmd version of the caller).

Is it done for migrate? Surely it's not for swapout ;).

> Thanks for viewing!

You're welcome!

JFYI I'll be offline on vacation for a week, starting tomorrow, so if
I don't answer in the next few days that's the reason but I'll follow
the progress in a week.

Thanks!
Andrea
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