From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from out02.mta.xmission.com ([166.70.13.232]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1cFDeL-0005rI-Cl for kexec@lists.infradead.org; Fri, 09 Dec 2016 05:23:14 +0000 From: ebiederm@xmission.com (Eric W. Biederman) References: <1481164674-42775-1-git-send-email-zhongjiang@huawei.com> <58492ADC.4070305@redhat.com> <584A3D84.6040004@huawei.com> Date: Fri, 09 Dec 2016 18:19:37 +1300 In-Reply-To: <584A3D84.6040004@huawei.com> (zhong jiang's message of "Fri, 9 Dec 2016 13:13:40 +0800") Message-ID: <87inqtn0gm.fsf@xmission.com> MIME-Version: 1.0 Subject: Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages 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: zhong jiang Cc: Xunlei Pang , akpm@linux-foundation.org, xlpang@redhat.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org 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 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec