From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: broken VM in 2.4.10-pre9 References: <20010925005033.A137@bug.ucw.cz> <20010927014431.C2164@bug.ucw.cz> From: ebiederm@xmission.com (Eric W. Biederman) Date: 27 Sep 2001 07:52:43 -0600 In-Reply-To: <20010927014431.C2164@bug.ucw.cz> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: Pavel Machek Cc: Marcelo Tosatti , Alan Cox , Daniel Phillips , Rob Fuller , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Pavel Machek writes: > Hi! > > > > > > So my suggestion was to look at getting anonymous pages backed by what > > > > > amounts to a shared memory segment. In that vein. By using an extent > > > > > based data structure we can get the cost down under the current 8 bits > > > > > per page that we have for the swap counts, and make allocating swap > > > > > pages faster. And we want to cluster related swap pages anyway so > > > > > an extent based system is a natural fit. > > > > > > > > Much of this goes away if you get rid of both the swap and anonymous page > > > > special cases. Back anonymous pages with the "whoops everything I write > here > > > > > vanishes mysteriously" file system and swap with a swapfs > > > > > > What exactly is anonymous memory? I thought it is what you do when you > > > want to malloc(), but you want to back that up by swap, not /dev/null. > > > > Anonymous memory is memory which is not backed by a filesystem or a > > device. eg: malloc()ed memory, shmem, mmap(MAP_PRIVATE) on a file (which > > will create anonymous memory as soon as the program which did the mmap > > writes to the mapped memory (COW)), etc. > > So... how can alan propose to back anonymous memory with /dev/null? > [see above] It should be backed by swap, no? He's not. Alan if I understand him correctly is advocating remove special cases. And making it look like all pages are backed by something. The /dev/nullfs is just until swap is allocated for that page. I don't agree with the exact details of what Alan is envsions but I do argree with the basic idea... Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/