Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755362AbbFLWsc (ORCPT ); Fri, 12 Jun 2015 18:48:32 -0400 Received: from g9t5008.houston.hp.com ([15.240.92.66]:54063 "EHLO g9t5008.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753481AbbFLWs3 (ORCPT ); Fri, 12 Jun 2015 18:48:29 -0400 Message-ID: <557B61B7.4080301@hp.com> Date: Fri, 12 Jun 2015 18:48:23 -0400 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Ingo Molnar CC: linux-kernel@vger.kernel.org, linux-mml@vger.kernel.org, Andy Lutomirski , Andrew Morton , Denys Vlasenko , Brian Gerst , Peter Zijlstra , Borislav Petkov , "H. Peter Anvin" , Linus Torvalds , Oleg Nesterov , Thomas Gleixner Subject: Re: [PATCH 02/12] x86/mm/hotplug: Remove pgd_list use from the memory hotplug code References: <1434031637-9091-1-git-send-email-mingo@kernel.org> <1434031637-9091-3-git-send-email-mingo@kernel.org> In-Reply-To: <1434031637-9091-3-git-send-email-mingo@kernel.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3429 Lines: 89 On 06/11/2015 10:07 AM, Ingo Molnar wrote: > The memory hotplug code uses sync_global_pgds() to synchronize updates > to the global (&init_mm) kernel PGD and the task PGDs. It does this > by iterating over the pgd_list - which list closely tracks task > creation/destruction via fork/clone. > > But we want to remove this list, so that it does not have to be > maintained from fork()/exit(), so convert the memory hotplug code > to use the task list to iterate over all pgds in the system. > > Also improve the comments a bit, to make this function easier > to understand. > > Only lightly tested, as I don't have a memory hotplug setup. > > Cc: Andrew Morton > Cc: Andy Lutomirski > Cc: Borislav Petkov > Cc: Brian Gerst > Cc: Denys Vlasenko > Cc: H. Peter Anvin > Cc: Linus Torvalds > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: Waiman Long > Signed-off-by: Ingo Molnar > --- > arch/x86/mm/init_64.c | 30 +++++++++++++++++------------- > 1 file changed, 17 insertions(+), 13 deletions(-) > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index 3fba623e3ba5..1921acbd49fd 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -160,8 +160,8 @@ static int __init nonx32_setup(char *str) > __setup("noexec32=", nonx32_setup); > > /* > - * When memory was added/removed make sure all the processes MM have > - * suitable PGD entries in the local PGD level page. > + * When memory was added/removed make sure all the process MMs have > + * matching PGD entries in the local PGD level page as well. > */ > void sync_global_pgds(unsigned long start, unsigned long end, int removed) > { > @@ -169,29 +169,33 @@ void sync_global_pgds(unsigned long start, unsigned long end, int removed) > > for (address = start; address<= end; address += PGDIR_SIZE) { > const pgd_t *pgd_ref = pgd_offset_k(address); > - struct page *page; > + struct task_struct *g, *p; > > /* > - * When it is called after memory hot remove, pgd_none() > - * returns true. In this case (removed == 1), we must clear > - * the PGD entries in the local PGD level page. > + * When this function is called after memory hot remove, > + * pgd_none() already returns true, but only the reference > + * kernel PGD has been cleared, not the process PGDs. > + * > + * So clear the affected entries in every process PGD as well: > */ > if (pgd_none(*pgd_ref)&& !removed) > continue; > > spin_lock(&pgd_lock); > - list_for_each_entry(page,&pgd_list, lru) { > - pgd_t *pgd; > + > + for_each_process_thread(g, p) { > + pgd_t *pgd = p->mm->pgd; > spinlock_t *pgt_lock; > > - pgd = (pgd_t *)page_address(page) + pgd_index(address); > - /* the pgt_lock only for Xen */ > - pgt_lock =&pgd_page_get_mm(page)->page_table_lock; > + if (!p->mm) > + continue; pgd was initialized to p->mm->pgd before the "p->mm" check is done. Shouldn't the initialization be moved after that. Cheers, Longman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/