From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 8 Mar 2005 15:04:24 +0000 (GMT) From: Mel Gorman Subject: Re: [PATCH] 2/2 Prezeroing large blocks of pages during allocation Version 4 In-Reply-To: <422D8F2A.4010002@jp.fujitsu.com> Message-ID: References: <20050307194021.E6A86E594@skynet.csn.ul.ie> <422D42BF.4060506@jp.fujitsu.com> <422D8F2A.4010002@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: KAMEZAWA Hiroyuki Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, clameter@sgi.com List-ID: On Tue, 8 Mar 2005, KAMEZAWA Hiroyuki wrote: > Mel Gorman wrote: > > > > > > > > Now, 5bits per MAX_ORDER pages. > > > I think it is simpler to use "char[]" for representing type of memory > > > alloc > > > type than bitmap. > > > > > > > > > > Possibly, but it would also use up that bit more space. That map could be > > condensed to 3 bits but would make it that bit (no pun) more complex and > > difficult to merge. On the other hand, it would be faster to use a char[] > > as it would be an array-index lookup to get a pageblock type rather than a > > number of bit operations. > > > > So, it depends on what people know to be better in general because I have > > not measured it to know for a fact. Is it better to use char[] and use > > array indexes rather than bit operations or is it better to leave it as a > > bitmap and condense it later when things have settled down? > > > Hmm, Okay, I'll wait for condensed version. > BTW, in space consumption/cache view, does using bitmap have real benefit > ? > For space, there is a small benefit. On my system with 1.5GiB of RAM, it is about 130 bytes saved for prezeroing and about 220 with just the placement policy. For speed, I do not know how bitmaps normally perform with the CPU cache, but for the placement policy, it makes no difference. I implemented a version using char[] array and there was no performance difference that I could measure. The bitmaps just are not consulted often enough to make a big performance difference. -- Mel Gorman Part-time Phd Student Java Applications Developer University of Limerick IBM Dublin Software Lab -- 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: aart@kvack.org