From mboxrd@z Thu Jan 1 00:00:00 1970 Message-Id: <20070525051716.030494061@sgi.com> Date: Thu, 24 May 2007 22:17:16 -0700 From: clameter@sgi.com Subject: [patch 0/6] Compound Page Enhancements Sender: owner-linux-mm@kvack.org Return-Path: To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, Mel Gorman , KAMEZAWA Hiroyuki , William Lee Irwin III List-ID: This patch enhances the handling of compound pages in the VM. It may also be important also for the antifrag patches that need to manage a set of higher order free pages and also for other uses of compound pages. For now it simplifies accounting for SLUB pages but the groundwork here is important for the large block size patches and for allowing to page migration of larger pages. With this framework we may be able to get to a point where compound pages keep their flags while they are free and Mel may avoid having special functions for determining the page order of higher order freed pages. If we can avoid the setup and teardown of higher order pages then allocation and release of compound pages will be faster. Looking at the handling of compound pages we see that the fact that a page is part of a higher order page is not that interesting. The differentiation is mainly for head pages and tail pages of higher order pages. Head pages usually need special handling to accomodate the larger size. It is usually an error if tail pages are encountered. Or else they need to be treated like PAGE_SIZE pages. So a compound flag in the page flags is not what we need. Instead we introduce a flag for the head page and another for the tail page. The PageCompound test is preserved for backward compatibility and will test if either PageTail or PageHead has been set. After this patchset the uses of CompoundPage() will be reduced significantly in the core VM. The I/O layer will still use CompoundPage() for direct I/O. However, if we at some point convert direct I/O to also support compound pages as a single unit then CompoundPage() there may become unecessary as well as the leftover check in mm/swap.c. We may end up mostly with checks for PageTail and PageHead. -- -- 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