From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 25 May 2007 06:54:24 -0700 (PDT) From: Christoph Lameter Subject: Re: [patch 0/6] Compound Page Enhancements In-Reply-To: <20070524230032.554be39e.akpm@linux-foundation.org> Message-ID: References: <20070525051716.030494061@sgi.com> <20070524230032.554be39e.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org, Mel Gorman , KAMEZAWA Hiroyuki , William Lee Irwin III List-ID: On Thu, 24 May 2007, Andrew Morton wrote: > Well I've read that, and I've read the patches and I still don't see what > the point in all this is. A. vmstat can handle compound pages. No need to determine the size of a compound page to update VM statistics. B. PageCompound is not useful in the long run. The processing of compound pages in the VM requires the knowledge if this is a head or tail page. That a page is part of a compound page is not that useful knowlege. C. Provide some more support for higher order page handling issues that Mel and I encounter. D. Compound pages may be useful to handle higher order blocks on the freelists if they can be handled efficiently. If we use the same format for the freelist as for compound pages elsewhere then we will have a common set of function to determine sizes etc etc. E. Expands usefulness of get_page_unless_zero to compound pages. This is necessary to allow the moving of slabs and the moving of higher order pages for memory defragmentation. F. Lays groundwork for large blocksize support. > And looking back on it, I don't see the point in that PG_head_tail_mask > hack either. We could have done > > static inline int page_tail(struct page *page) > { > return PageCompound(page) && (page->first_page != page); > } > > Confused. Don't know where this is all headed. To a better nicer looking VM. -- 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