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

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Message-ID: <20071220171143.GV19691@waste.org>
Date:	Thu, 20 Dec 2007 11:11:43 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Peter Zijlstra <peterz@...radead.org>
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, 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.

-- 
Mathematics is the supreme nostalgia of our time.
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