From: zhong jiang <zhongjiang@huawei.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <xlpang@redhat.com>, Xunlei Pang <xpang@redhat.com>,
<akpm@linux-foundation.org>, <kexec@lists.infradead.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages
Date: Fri, 9 Dec 2016 13:56:50 +0800 [thread overview]
Message-ID: <584A47A2.1040001@huawei.com> (raw)
In-Reply-To: <87inqtn0gm.fsf@xmission.com>
On 2016/12/9 13:19, Eric W. Biederman wrote:
> zhong jiang <zhongjiang@huawei.com> writes:
>
>> On 2016/12/8 17:41, Xunlei Pang wrote:
>>> On 12/08/2016 at 10:37 AM, zhongjiang wrote:
>>>> From: zhong jiang <zhongjiang@huawei.com>
>>>>
> [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
next prev parent reply other threads:[~2016-12-09 5:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 2:37 [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages zhongjiang
2016-12-08 3:22 ` Eric W. Biederman
2016-12-08 9:41 ` Xunlei Pang
2016-12-09 5:13 ` zhong jiang
2016-12-09 5:19 ` Eric W. Biederman
2016-12-09 5:56 ` zhong jiang [this message]
2016-12-09 7:16 ` Xunlei Pang
2016-12-19 3:23 ` Baoquan He
2016-12-21 5:06 ` Xunlei Pang
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