From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id DFA9F6B006A for ; Fri, 22 Jan 2010 11:52:23 -0500 (EST) Date: Fri, 22 Jan 2010 10:51:35 -0600 (CST) From: Christoph Lameter Subject: Re: [PATCH 00 of 30] Transparent Hugepage support #3 In-Reply-To: <20100122151947.GA3690@random.random> Message-ID: References: <20100122151947.GA3690@random.random> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli Cc: linux-mm@kvack.org, Marcelo Tosatti , Adam Litke , Avi Kivity , Izik Eidus , Hugh Dickins , Nick Piggin , Rik van Riel , Mel Gorman , Andi Kleen , Dave Hansen , Benjamin Herrenschmidt , Ingo Molnar , Mike Travis , KAMEZAWA Hiroyuki , Chris Wright , Andrew Morton List-ID: On Fri, 22 Jan 2010, Andrea Arcangeli wrote: > On Fri, Jan 22, 2010 at 08:46:50AM -0600, Christoph Lameter wrote: > > Jus thinking about yesterdays fix to page migration: > > > > This means that huge pages are unstable right? Kernel code cannot > > establish a reference to a 2M/4M page and be sure that the page is not > > broken up due to something in the VM that cannot handle huge pages? > > Physically speaking DMA-wise they cannot be broken up, only thing that > gets broken up is the pmd that instead of mapping the page directly > starts to map the pte. Nothing changes on the physical side of > hugepages. khugepaged only collapse pages into hugepages if there are > no references at all (no gup no nothing) so again no issue DMA-wise. Reclaim cannot kick out page size pieces of the huge page? > have irq disabled so the ipi of collapse_huge_page will wait. It's all > handled transparently by the patch, you won't notice you're dealing > with hugepage if you're gup user (unless you use gup to migrate pages > in which case calling split_huge_page is enough like in patch ;). What if I want to use hugepages for some purpose and I dont want to use 512 pointers to keep track of the individual pieces? -- 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