linux-kernel - Re: [rfc][patch] mm: madvise(WILLNEED) for anonymous memory

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Message-Id: <1198170959.30889.0.camel@lappy>
Date:	Thu, 20 Dec 2007 18:15:59 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Hugh Dickins <hugh@...itas.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Nick Piggin <npiggin@...e.de>,
	riel <riel@...hat.com>, Lennart Poettering <mztabzr@...inter.de>
Subject: Re: [rfc][patch] mm: madvise(WILLNEED) for anonymous memory


On Thu, 2007-12-20 at 11:11 -0600, Matt Mackall wrote:
> On Thu, Dec 20, 2007 at 05:53:41PM +0100, Peter Zijlstra wrote:
> > 
> > On Thu, 2007-12-20 at 15:26 +0000, Hugh Dickins wrote:
> > 
> > > The asynch code: perhaps not worth doing for MADV_WILLNEED alone,
> > > but might prove useful for more general use when swapping in.
> > > Not really the same as Con's swap prefetch, but worth looking
> > > at that for reference.  But I guess this becomes a much bigger
> > > issue than you were intending to get into here.
> > 
> > heh, yeah, got somewhat more complex that I'd hoped for.
> > 
> > last patch for today (not even compile tested), will do a proper patch
> > and test it tomorrow.
> > 
> > ---
> > A best effort MADV_WILLNEED implementation for anonymous memory.
> > 
> > It adds a batch method to the page table walk routines so we can
> > copy a few ptes while holding the kmap, which makes it possible to
> > allocate the backing pages using GFP_KERNEL.
> 
> Yuck. We actually need to just fix the atomic kmap issue in the
> existing pagemap code rather than add a new method, I think.
> 
> If performance of map/unmap is too slow at a granularity of 1, we can
> add some internal batching in the CONFIG_HIGHPTE case.

OK, sounds like a much better idea indeed. Will implement that.

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