From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [PATCH 1/1] handle initialising compound pages at orders greater than MAX_ORDER Date: Fri, 3 Oct 2008 16:43:28 +1000 References: <1222964396-25031-1-git-send-email-apw@shadowen.org> <20081002143004.5fec3952.akpm@linux-foundation.org> In-Reply-To: <20081002143004.5fec3952.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200810031643.28731.nickpiggin@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Andy Whitcroft , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kniht@linux.vnet.ibm.com, mel@csn.ul.ie List-ID: On Friday 03 October 2008 07:30, Andrew Morton wrote: > On Thu, 2 Oct 2008 17:19:56 +0100 > > Andy Whitcroft wrote: > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -268,13 +268,14 @@ void prep_compound_page(struct page *page, unsigned > > long order) { > > int i; > > int nr_pages = 1 << order; > > + struct page *p = page + 1; > > > > set_compound_page_dtor(page, free_compound_page); > > set_compound_order(page, order); > > __SetPageHead(page); > > - for (i = 1; i < nr_pages; i++) { > > - struct page *p = page + i; > > - > > + for (i = 1; i < nr_pages; i++, p++) { > > + if (unlikely((i & (MAX_ORDER_NR_PAGES - 1)) == 0)) > > + p = pfn_to_page(page_to_pfn(page) + i); > > __SetPageTail(p); > > p->first_page = page; > > } > > gad. Wouldn't it be clearer to do > > for (i = 1; i < nr_pages; i++) { > struct page *p = pfn_to_page(i); > __SetPageTail(p); > p->first_page = page; > } > > Oh well, I guess we can go with the obfuscated, uncommented version for > now :( > > This patch applies to 2.6.26 (and possibly earlier) but I don't think > those kernels can trigger the bug? I think the problem is that pfn_to_page isn't always trivial. I would prefer to have seen a new function for hugetlb to use, and keep the branch-less version for the page allocator itself. -- 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