To: rmk+lkml@arm.linux.org.uk
CC: davem@davemloft.net, arjan@infradead.org, torvalds@osdl.org,
       linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, akpm@osdl.org
In-reply-to: <20061231173743.GD1702@flint.arm.linux.org.uk> (message from
	Russell King on Sun, 31 Dec 2006 17:37:43 +0000)
Subject: Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again
References: <20061230.212338.92583434.davem@davemloft.net> <20061231092318.GA1702@flint.arm.linux.org.uk> <1167557242.20929.647.camel@laptopd505.fenrus.org> <20061231.014756.112264804.davem@davemloft.net> <20061231100007.GC1702@flint.arm.linux.org.uk> <E1H0zkD-0003uw-00@dorka.pomaz.szeredi.hu> <20061231173743.GD1702@flint.arm.linux.org.uk>
Message-Id: <E1H1VQu-0005oJ-00@dorka.pomaz.szeredi.hu>
From: Miklos Szeredi <miklos@szeredi.hu>
Date: Mon, 01 Jan 2007 23:15:04 +0100
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1644
Lines: 39

> > > I'm willing to do that - and I guess this means we can probably do this
> > > instead of walking the list of VMAs for the shared mapping, thereby
> > > hitting both anonymous and shared mappings with the same code?
> > 
> > But for the get_user_pages() case there's no point, is there?  The VMA
> > and the virtual address is already available, so trying to find it
> > again through RMAP doesn't much make sense.
> > 
> > Users of get_user_pages() don't care about any other mappings (maybe
> > ptrace does, I don't know) only about one single user mapping and one
> > kernel mapping.
> > 
> > So using flush_dcache_page() there is an overkill, trying to teach it
> > about anonymous pages is not the real solution, flush_dcache_page()
> > was never meant to be used on anything but file mapped pages.
> 
> It's not actually.  For flush_anon_page() we currently have to flush the
> user mapping and the kernel mapping.  For flush_dcache_page(), it's
> exactly the same - we have to flush the kernel mapping and the user
> mapping.

I was never advocating flush_anon_page().  I was suggesting a _new_
cache operation:

   flush_kernel_user_page(page, vma, virt_addr)

which flushes the kernel mapping and the given user mapping.  Just
like flush_dcache_page() but without needing to find the user
mapping(s).

However the cache flushing in kmap/kunmap idea might be cleaner and
better.

Miklos
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