From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 7EE6A6B01AC for ; Wed, 2 Jun 2010 19:34:46 -0400 (EDT) Date: Wed, 2 Jun 2010 16:33:46 -0700 From: Andrew Morton Subject: Re: [PATCH] hugetlb: call mmu notifiers on hugepage cow Message-Id: <20100602163346.b8f8b8a4.akpm@linux-foundation.org> In-Reply-To: <4C06E5A6.6@cray.com> References: <4BFED954.8060807@cray.com> <20100601231600.3b3bf499.akpm@linux-foundation.org> <4C06E5A6.6@cray.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Doug Doan Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "andi@firstfloor.org" , "lee.schermerhorn@hp.com" , "rientjes@google.com" , "mel@csn.ul.ie" , Andrea Arcangeli List-ID: On Wed, 2 Jun 2010 16:13:42 -0700 Doug Doan wrote: > On 06/01/2010 11:16 PM, Andrew Morton wrote: > > On Thu, 27 May 2010 13:43:00 -0700 Doug Doan wrote: > > > >> > >> When a copy-on-write occurs, we take one of two paths in handle_mm_fault: > >> through handle_pte_fault for normal pages, or through hugetlb_fault for huge pages. > >> > >> In the normal page case, we eventually get to do_wp_page and call mmu notifiers > >> via ptep_clear_flush_notify. There is no callout to the mmmu notifiers in the > >> huge page case. This patch fixes that. > >> > >> Signed-off-by: Doug Doan > >> --- > >> > >> [patch text/plain (802B)] > >> --- mm/hugetlb.c.orig 2010-05-27 13:07:58.569546314 -0700 > >> +++ mm/hugetlb.c 2010-05-26 14:41:06.449296524 -0700 > > > > (In patch -p1 form, please. So a/mm/hugetlb.c) > > > >> @@ -2345,11 +2345,17 @@ retry_avoidcopy: > >> ptep = huge_pte_offset(mm, address& huge_page_mask(h)); > >> if (likely(pte_same(huge_ptep_get(ptep), pte))) { > >> /* Break COW */ > >> + mmu_notifier_invalidate_range_start(mm, > >> + address& huge_page_mask(h), > >> + (address& huge_page_mask(h)) + huge_page_size(h)); > >> huge_ptep_clear_flush(vma, address, ptep); > >> set_huge_pte_at(mm, address, ptep, > >> make_huge_pte(vma, new_page, 1)); > >> /* Make the old page be freed below */ > >> new_page = old_page; > >> + mmu_notifier_invalidate_range_end(mm, > >> + address& huge_page_mask(h), > >> + (address& huge_page_mask(h)) + huge_page_size(h)); > >> } > >> page_cache_release(new_page); > >> page_cache_release(old_page); > > > > This causes mmu_notifier_invalidate_range_start() to be called under > > page_table_lock. The immediately preceding code seems to take some > > care to avoid doing that. I took a quick look at other callsites and > > cannot immediately see other cases where > > mmu_notifier_invalidate_range_start/end() are called under that lock. > > > > This may not introduce bugs with current notifier implementations (I > > didn't check), but it does lessen flexibility? > > In the normal page case, handle_pte_fault calls do_wp_page inside a spinlock on > ptl = pte_lockptr(mm, pmd), which uses mm->page_table_lock if USE_SPLIT_PTLOCKS > is not defined. > > I don't understand what you mean by lessen flexibilty. Well, specifically it means that mmu_notifier_invalidate_range_start/end() implemetnations can no longer take page_table_lock or any lock which nests outside page_table_lock. That lessens flexibility. As the other mmu_notifier_invalidate_range_start/end() callsite in this function carefully nested those calls outside page_table_lock, perhaps that was thought to be a significant thing. -- 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