From mboxrd@z Thu Jan 1 00:00:00 1970 From: mina86@mina86.com (Michal Nazarewicz) Date: Mon, 12 Dec 2011 15:51:55 +0100 Subject: [PATCH 03/11] mm: mmzone: introduce zone_pfn_same_memmap() In-Reply-To: <20111212144030.GF3277@csn.ul.ie> References: <1321634598-16859-1-git-send-email-m.szyprowski@samsung.com> <1321634598-16859-4-git-send-email-m.szyprowski@samsung.com> <20111212141953.GD3277@csn.ul.ie> <20111212144030.GF3277@csn.ul.ie> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > On Fri, Nov 18, 2011 at 05:43:10PM +0100, Marek Szyprowski wrote: >> From: Michal Nazarewicz >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 6afae0e..09c9702 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -111,7 +111,10 @@ skip: >> >> next: >> pfn += isolated; >> - page += isolated; >> + if (zone_pfn_same_memmap(pfn - isolated, pfn)) >> + page += isolated; >> + else >> + page = pfn_to_page(pfn); >> } On Mon, 12 Dec 2011 15:19:53 +0100, Mel Gorman wrote: > Is this necessary? > > We are isolating pages, the largest of which is a MAX_ORDER_NR_PAGES > page. [...] On Mon, 12 Dec 2011 15:40:30 +0100, Mel Gorman wrote: > To be clear, I'm referring to a single page being isolated here. It may > or may not be a high-order page but it's still going to be less then > MAX_ORDER_NR_PAGES so you should be able check when a new block is > entered and pfn_to_page is necessary. Do you mean something like: if (same pageblock) just do arithmetic; else use pfn_to_page; ? I've discussed it with Dave and he suggested that approach as an optimisation since in some configurations zone_pfn_same_memmap() is always true thus compiler will strip the else part, whereas same pageblock test will be false on occasions regardless of kernel configuration. -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Micha? ?mina86? Nazarewicz (o o) ooo +------------------ooO--(_)--Ooo--