From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from szxga03-in.huawei.com ([119.145.14.66]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1cFEBt-0002DT-60 for kexec@lists.infradead.org; Fri, 09 Dec 2016 05:57:56 +0000 Message-ID: <584A47A2.1040001@huawei.com> Date: Fri, 9 Dec 2016 13:56:50 +0800 From: zhong jiang MIME-Version: 1.0 Subject: Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages References: <1481164674-42775-1-git-send-email-zhongjiang@huawei.com> <58492ADC.4070305@redhat.com> <584A3D84.6040004@huawei.com> <87inqtn0gm.fsf@xmission.com> In-Reply-To: <87inqtn0gm.fsf@xmission.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: "Eric W. Biederman" Cc: Xunlei Pang , akpm@linux-foundation.org, xlpang@redhat.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org On 2016/12/9 13:19, Eric W. Biederman wrote: > zhong jiang writes: > >> On 2016/12/8 17:41, Xunlei Pang wrote: >>> On 12/08/2016 at 10:37 AM, zhongjiang wrote: >>>> From: zhong jiang >>>> > [snip] >>>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c >>>> index 5616755..bfc9621 100644 >>>> --- a/kernel/kexec_core.c >>>> +++ b/kernel/kexec_core.c >>>> @@ -441,6 +441,8 @@ static struct page *kimage_alloc_crash_control_pages(struct kimage *image, >>>> while (hole_end <= crashk_res.end) { >>>> unsigned long i; >>>> >>>> + cond_resched(); >>>> + >>> I can't see why it would take a long time to loop inside, the job it does is simply to find a control area >>> not overlapped with image->segment[], you can see the loop "for (i = 0; i < image->nr_segments; i++)", >>> @hole_end will be advanced to the end of its next nearby segment once overlap was detected each loop, >>> also there are limited (<=16) segments, so it won't take long to locate the right area. >>> >>> Am I missing something? >>> >>> Regards, >>> Xunlei >> if the crashkernel = auto is set in cmdline. it represent crashk_res.end will exceed to 4G, the first allocate control pages will >> loop million times. if we set crashk_res.end to the higher value >> manually, you can image.... > Or in short the cond_resched is about keeping things reasonable when the > loop has worst case behavior. > > Eric > > Yes, Thank you reply and comment. Regards, zhongjiang _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec