linux-kernel - Re: ARM: vmsplit 4g/4g

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Message-ID: <20200607161116.GN1551@shell.armlinux.org.uk>
Date:   Sun, 7 Jun 2020 17:11:16 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     afzal mohammed <afzal.mohd.ma@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: ARM: vmsplit 4g/4g

On Sun, Jun 07, 2020 at 06:29:32PM +0530, afzal mohammed wrote:
> Hi,
> 
> On Sat, May 16, 2020 at 09:35:57AM +0200, Arnd Bergmann wrote:
> > On Sat, May 16, 2020 at 8:06 AM afzal mohammed <afzal.mohd.ma@...il.com> wrote:
> 
> > > Okay, so the conclusion i take is,
> > > 1. VMSPLIT 4G/4G have to live alongside highmem
> > > 2. For user space copy, do pinning followed by kmap
> 
> > Right, though kmap_atomic() should be sufficient here
> > because it is always a short-lived mapping.
> 
> get_user_pages_fast() followed by kmap_atomic() & then memcpy() seems
> to work in principle for user copy.

Have you done any performance evaluation of the changes yet? I think
it would be a good idea to keep that in the picture. If there's any
significant regression, then that will need addressing.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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