Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751066AbWAPQCV (ORCPT ); Mon, 16 Jan 2006 11:02:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751073AbWAPQCV (ORCPT ); Mon, 16 Jan 2006 11:02:21 -0500 Received: from elvis.mu.org ([192.203.228.196]:3326 "EHLO elvis.mu.org") by vger.kernel.org with ESMTP id S1751065AbWAPQCU (ORCPT ); Mon, 16 Jan 2006 11:02:20 -0500 Message-ID: <43CBC37F.60002@FreeBSD.org> Date: Mon, 16 Jan 2006 08:02:07 -0800 From: Suleiman Souhlal User-Agent: Mozilla Thunderbird 1.0.7 (X11/20051204) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrea Arcangeli CC: Badari Pulavarty , Andrew Morton , linux-kernel@vger.kernel.org, hugh@veritas.com, dvhltc@us.ibm.com, linux-mm@kvack.org, blaisorblade@yahoo.it, jdike@addtoit.com Subject: Re: differences between MADV_FREE and MADV_DONTNEED References: <20051029025119.GA14998@ccure.user-mode-linux.org> <1130788176.24503.19.camel@localhost.localdomain> <20051101000509.GA11847@ccure.user-mode-linux.org> <1130894101.24503.64.camel@localhost.localdomain> <20051102014321.GG24051@opteron.random> <1130947957.24503.70.camel@localhost.localdomain> <20051111162511.57ee1af3.akpm@osdl.org> <1131755660.25354.81.camel@localhost.localdomain> <20051111174309.5d544de4.akpm@osdl.org> <43757263.2030401@us.ibm.com> <20060116130649.GE15897@opteron.random> In-Reply-To: <20060116130649.GE15897@opteron.random> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2024 Lines: 46 Andrea Arcangeli wrote: > Now that MADV_REMOVE is in, should we discuss MADV_FREE? > > MADV_FREE in Solaris is destructive and only works on anonymous memory, > while MADV_DONTNEED seems to never be destructive (which I assume it > means it's a noop on anonymous memory). FWIW, in FreeBSD, MADV_DONTNEED is not destructive, and just makes pages (including anonymous ones) more likely to get swapped out. > Our MADV_DONTNEED is destructive on anonymous memory, while it's > non-destructive on file mappings. > > Perhaps we could move the destructive anonymous part of MADV_DONTNEED to > MADV_FREE? This would seem like the best way to go, since it would bring Linux's behavior more in line with what other systems do. > Or we could as well go relaxed and define MADV_FREE and MADV_DONTNEED > the same way (that still leaves the question if we risk to break apps > ported from solaris where MADV_DONTNEED is apparently always not > destructive). > > I only read the docs, I don't know in practice what MADV_DONTNEED does > on solaris (does it return -EINVAL if run on anonymous memory or not?). > > http://docs.sun.com/app/docs/doc/816-5168/6mbb3hrgk?a=view > > BTW, I don't know how other specifications define MADV_FREE, but besides > MADV_REMOVE I've also got the request to provide MADV_FREE in linux, > this is why I'm asking. (right now I'm telling them to use #ifdef > __linux__ #define MADV_FREE MADV_DONTNEED but that's quite an hack since > it could break if we make MADV_DONTNEED non-destructive in the future) FreeBSD's MADV_FREE only works on anonymous memory (it's a noop for vnode-backed memory), and marks the pages clean before moving them to the inactive queue, so that they can be freed or reused quickly, without causing a pagefault. -- Suleiman - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/