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

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Message-ID: <20071220162902.GA1945@tango.0pointer.de>
Date:	Thu, 20 Dec 2007 17:29:02 +0100
From:	Lennart Poettering <mzxreary@...inter.de>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Nick Piggin <npiggin@...e.de>,
	riel <riel@...hat.com>
Subject: Re: [rfc][patch] mm: madvise(WILLNEED) for anonymous memory

On Thu, 20.12.07 14:09, Hugh Dickins (hugh@...itas.com) wrote:

> > Lennart asked for madvise(WILLNEED) to work on anonymous pages, he plans
> > to use this to pre-fault pages. He currently uses: mlock/munlock for
> > this purpose.
> 
> I certainly agree with this in principle: it just seems an unnecessary
> and surprising restriction to refuse on anonymous vmas; I guess the only
> reason for not adding this was not having anyone asking for it until now.
> Though, does Lennart realize he could use MAP_POPULATE in the mmap?

Not really. First, if the mmap() is hidden somewhere in glibc (i.e. as
part of malloc() or whatever) it's not really possible to do
MAP_POPULATE. Also, I need this for some memory that is allocated
during the whole runtime but only seldomly used. Thus I am happy if it
is swapped out, but everytime I want to use it I want to make sure it
is paged in before I pass it on to the RT thread. So, there's a
mmap() during startup only, and then, during the whole runtime of my
program I want to page in the memory again and again, with long
intervals in between, but with no call to mmap()/munmap().

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4
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