From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752655AbZHMGSq (ORCPT ); Thu, 13 Aug 2009 02:18:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751970AbZHMGSo (ORCPT ); Thu, 13 Aug 2009 02:18:44 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:50569 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751222AbZHMGSn (ORCPT ); Thu, 13 Aug 2009 02:18:43 -0400 To: Amerigo Wang Cc: linux-kernel@vger.kernel.org, tony.luck@intel.com, linux-ia64@vger.kernel.org, linux-mm@kvack.org, Neil Horman , Andi Kleen , akpm@linux-foundation.org, bernhard.walle@gmx.de, Fenghua Yu , Ingo Molnar , Anton Vorontsov References: <20090812081731.5757.25254.sendpatchset@localhost.localdomain> <20090812081906.5757.39417.sendpatchset@localhost.localdomain> <4A83893D.50707@redhat.com> From: ebiederm@xmission.com (Eric W. Biederman) Date: Wed, 12 Aug 2009 23:18:33 -0700 In-Reply-To: <4A83893D.50707@redhat.com> (Amerigo Wang's message of "Thu\, 13 Aug 2009 11\:32\:13 +0800") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in02.mta.xmission.com;;;ip=76.21.114.89;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 76.21.114.89 X-SA-Exim-Rcpt-To: amwang@redhat.com, avorontsov@ru.mvista.com, mingo@elte.hu, fenghua.yu@intel.com, bernhard.walle@gmx.de, akpm@linux-foundation.org, andi@firstfloor.org, nhorman@redhat.com, linux-mm@kvack.org, linux-ia64@vger.kernel.org, tony.luck@intel.com, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa02 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Amerigo Wang X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -2.6 BAYES_00 BODY: Bayesian spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa02 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 XM_SPF_Neutral SPF-Neutral * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay Subject: Re: [Patch 8/8] kexec: allow to shrink reserved memory X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Amerigo Wang writes: > Eric W. Biederman wrote: >> Amerigo Wang writes: >> >> >>> This patch implements shrinking the reserved memory for crash kernel, >>> if it is more than enough. >>> >>> For example, if you have already reserved 128M, now you just want 100M, >>> you can do: >>> >>> # echo $((100*1024*1024)) > /sys/kernel/kexec_crash_size >>> >> >> Getting closer (comments inline) >> >> Semantically this patch is non-contriversial and pretty >> simple, but still needs a fair amount of review. Can >> you put this patch at the front of your patch set. >> >> > > Sure, I will do it when I resend them next time. > > I add mm people into Cc. >>> Index: linux-2.6/kernel/kexec.c >>> =================================================================== >>> --- linux-2.6.orig/kernel/kexec.c >>> +++ linux-2.6/kernel/kexec.c >>> @@ -1083,6 +1083,76 @@ void crash_kexec(struct pt_regs *regs) >>> } >>> } >>> +int kexec_crash_kernel_loaded(void) >>> +{ >>> + int ret; >>> + if (!mutex_trylock(&kexec_mutex)) >>> + return 1; >>> >> >> We don't need trylock on this code path > > OK. > >> >>> + ret = kexec_crash_image != NULL; >>> + mutex_unlock(&kexec_mutex); >>> + return ret; >>> +} >>> + >>> +size_t get_crash_memory_size(void) >>> +{ >>> + size_t size; >>> + if (!mutex_trylock(&kexec_mutex)) >>> + return 1; >>> >> >> We don't need trylock on this code path >> >> > > Hmm, crashk_res is a global struct, so other process can also > change it... but currently no process does that, right? > We still need the lock. Just doing trylock doesn't instead of just sleeping doesn't seem to make any sense on these code paths. >>> + size = crashk_res.end - crashk_res.start + 1; >>> + mutex_unlock(&kexec_mutex); >>> + return size; >>> +} >>> + >>> +int shrink_crash_memory(unsigned long new_size) >>> +{ >>> + struct page **pages; >>> + int ret = 0; >>> + int npages, i; >>> + unsigned long addr; >>> + unsigned long start, end; >>> + void *vaddr; >>> + >>> + if (!mutex_trylock(&kexec_mutex)) >>> + return -EBUSY; >>> >> >> We don't need trylock on this code path >> >> We are missing the check to see if the crash_kernel is loaded >> under this lock instance. So I please move the kexec_crash_image != NULL >> test inline here and kill the kexec_crash_kernel_loaded function. >> > > Ok, no problem. > >> >>> + start = crashk_res.start; >>> + end = crashk_res.end; >>> + >>> + if (new_size >= end - start + 1) { >>> + ret = -EINVAL; >>> + if (new_size == end - start + 1) >>> + ret = 0; >>> + goto unlock; >>> + } >>> + >>> + start = roundup(start, PAGE_SIZE); >>> + end = roundup(start + new_size, PAGE_SIZE) - 1; >>> + npages = (end + 1 - start ) / PAGE_SIZE; >>> + >>> + pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL); >>> + if (!pages) { >>> + ret = -ENOMEM; >>> + goto unlock; >>> + } >>> + for (i = 0; i < npages; i++) { >>> + addr = end + 1 + i * PAGE_SIZE; >>> + pages[i] = virt_to_page(addr); >>> + } >>> + >>> + vaddr = vm_map_ram(pages, npages, 0, PAGE_KERNEL); >>> >> >> This is the wrong kernel call to use. I expect this needs to look >> like a memory hotplug event. This does not put the pages into the >> free page pool. >> > > Well, I also wanted to use an memory-hotplug API, but that will make the code > depend on memory-hotplug, which certainly is not what we want... > > I checked the mm code, actually what I need is an API which is similar to > add_active_range(), but add_active_range() can't be used here since it is marked > as "__init". > > Do we have that kind of API in mm? I can't find one. Perhaps we will need to remove __init from add_active_range. I know the logic but I'm not up to speed on the mm pieces at the moment. Eric