linux-kernel - Re: [PATCH RFC] vmalloc: eagerly clear ptes on vunmap

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Message-Id: <20101130162938.8a6b0df4.akpm@linux-foundation.org>
Date:	Tue, 30 Nov 2010 16:29:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Nick Piggin <npiggin@...nel.dk>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Bryan Schumaker <bjschuma@...app.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH RFC] vmalloc: eagerly clear ptes on vunmap

On Mon, 29 Nov 2010 12:32:11 -0800
Jeremy Fitzhardinge <jeremy@...p.org> 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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