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[Xen-devel] Re: [PATCH RFC] vmalloc: eagerly clear ptes on vunmap

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH RFC] vmalloc: eagerly clear ptes on vunmap
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Date: Tue, 30 Nov 2010 16:29:38 -0800
Cc: Bryan, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Schumaker <bjschuma@xxxxxxxxxx>, Linux Memory Management List <linux-mm@xxxxxxxxx>
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On Mon, 29 Nov 2010 12:32:11 -0800
Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

> When unmapping a region in the vmalloc space, clear the ptes immediately.
> There's no point in deferring this because there's no amortization
> benefit.
> The TLBs are left dirty, and they are flushed lazily to amortize the
> cost of the IPIs.
> This specific motivation for this patch is a regression since 2.6.36 when
> using NFS under Xen, triggered by the NFS client's use of vm_map_ram()
> introduced in 56e4ebf877b6043c289bda32a5a7385b80c17dee.  XFS also uses
> vm_map_ram() and could cause similar problems.

Do we have any quantitative info on that regression?  The patch fixed
it, I assume?

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