From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by uproxy.gmail.com with SMTP id k40so79215ugc for ; Wed, 08 Feb 2006 23:00:47 -0800 (PST) Message-ID: Date: Thu, 9 Feb 2006 16:00:47 +0900 From: Magnus Damm Subject: Re: [PATCH] Dynamically allocated pageflags In-Reply-To: <200602022111.32930.ncunningham@cyclades.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Content-Disposition: inline References: <200602022111.32930.ncunningham@cyclades.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Nigel Cunningham Cc: linux-mm , linux-kernel@vger.kernel.org List-ID: Hi Nigel, On 2/2/06, Nigel Cunningham wrote: > Hi everyone. > > This is my latest revision of the dynamically allocated pageflags patch. > > The patch is useful for kernel space applications that sometimes need to flag > pages for some purpose, but don't otherwise need the retain the state. A prime > example is suspend-to-disk, which needs to flag pages as unsaveable, allocated > by suspend-to-disk and the like while it is working, but doesn't need to > retain any of this state between cycles. > > Since the last revision, I have switched to using per-zone bitmaps within each > bitmap. > > I know that I could still add hotplug memory support. Is there anything else > missing? I like the idea of the patch, but the code looks a bit too complicated IMO. What is wrong with using vmalloc() to allocate a virtual contiguous range of 0-order pages (one bit per page), and then use the functions in linux/bitmap.h...? Or maybe I'm misunderstanding. A system that has 2 GB RAM and 4 KB pages would use 64 KB per bitmap (one bitmap per node), which is not so bad memory wise if you plan to use all bits. OTOH, if your plan is to use a single bit here and there, and leave most of the bits unused then some kind of tree is probably better. Or does the kernel already implement some kind of data structure that never consumes _that_ much more space than a bitmap when fully used, and saves a lot of memory when just sparsely populated? / magnus -- 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/ . Don't email: email@kvack.org