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Message-ID: <Pine.LNX.4.64.0704210830310.26485@blonde.wat.veritas.com>
Date: Sat, 21 Apr 2007 08:37:03 +0100 (BST)
From: Hugh Dickins <hugh@...itas.com>
To: Ulrich Drepper <drepper@...il.com>
cc: Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>,
Jakub Jelinek <jakub@...hat.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] lazy freeing of memory through MADV_FREE 2/2
On Fri, 20 Apr 2007, Ulrich Drepper wrote:
>
> Just for reference: the MADV_CURRENT behavior is to throw away data in
> the range.
Not exactly. The Linux MADV_DONTNEED never throws away data from a
PROT_WRITE,MAP_SHARED mapping (or shm) - it propagates the dirty bit,
the page will eventually get written out to file, and can be retrieved
later by subsequent access. But the Linux MADV_DONTNEED does throw away
data from a PROT_WRITE,MAP_PRIVATE mapping (or brk or stack) - those
changes are discarded, and a subsequent access will revert to zeroes
or the underlying mapped file. Been like that since before 2.4.0.
> The POSIX_MADV_DONTNEED behavior is to never lose data.
> I.e., file backed data is written back, anon data is at most swapped
> out.
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