From: chenzhou <chenzhou10@huawei.com>
To: Bhupesh Sharma <bhsharma@redhat.com>,
Catalin Marinas <catalin.marinas@arm.com>
Cc: Simon Horman <horms@verge.net.au>,
John Donnelly <john.p.donnelly@oracle.com>,
guohanjun@huawei.com, xiexiuqi@huawei.com,
Arnd Bergmann <arnd@arndb.de>, Baoquan He <bhe@redhat.com>,
Jonathan Corbet <corbet@lwn.net>, Will Deacon <will@kernel.org>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>,
kexec mailing list <kexec@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Rob Herring <robh+dt@kernel.org>,
wangkefeng.wang@huawei.com, Ingo Molnar <mingo@redhat.com>,
James Morse <james.morse@arm.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
huawei.libin@huawei.com,
Prabhakar Kushwaha <prabhakar.pkin@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
RuiRui Yang <dyoung@redhat.com>,
nsaenzjulienne@suse.de
Subject: Re: [PATCH v12 0/9] support reserving crashkernel above 4G on arm64 kdump
Date: Mon, 19 Oct 2020 10:43:05 +0800 [thread overview]
Message-ID: <ab142d7d-55a7-eca6-4609-147e1605f02d@huawei.com> (raw)
In-Reply-To: <CACi5LpMmccLX9p0ZXnEbWHgn2LRrVSDQZF9zBGzfZySe3TvXEQ@mail.gmail.com>
Hi Bhupesh,
On 2020/10/7 15:07, Bhupesh Sharma wrote:
> Hi Catalin,
>
> On Tue, Oct 6, 2020 at 11:30 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>> On Mon, Oct 05, 2020 at 11:12:10PM +0530, Bhupesh Sharma wrote:
>>> I think my earlier email with the test results on this series bounced
>>> off the mailing list server (for some weird reason), but I still see
>>> several issues with this patchset. I will add specific issues in the
>>> review comments for each patch again, but overall, with a crashkernel
>>> size of say 786M, I see the following issue:
>>>
>>> # cat /proc/cmdline
>>> BOOT_IMAGE=(hd7,gpt2)/vmlinuz-5.9.0-rc7+ root=<..snip..> rd.lvm.lv=<..snip..> crashkernel=786M
>>>
>>> I see two regions of size 786M and 256M reserved in low and high
>>> regions respectively, So we reserve a total of 1042M of memory, which
>>> is an incorrect behaviour:
>>>
>>> # dmesg | grep -i crash
>>> [ 0.000000] Reserving 256MB of low memory at 2816MB for crashkernel (System low RAM: 768MB)
>>> [ 0.000000] Reserving 786MB of memory at 654158MB for crashkernel (System RAM: 130816MB)
>>> [ 0.000000] Kernel command line: BOOT_IMAGE=(hd2,gpt2)/vmlinuz-5.9.0-rc7+ root=/dev/mapper/rhel_ampere--hr330a--03-root ro rd.lvm.lv=rhel_ampere-hr330a-03/root rd.lvm.lv=rhel_ampere-hr330a-03/swap crashkernel=786M cma=1024M
>>>
>>> # cat /proc/iomem | grep -i crash
>>> b0000000-bfffffff : Crash kernel (low)
>>> bfcbe00000-bffcffffff : Crash kernel
>> As Chen said, that's the intended behaviour and how x86 works. The
>> requested 768M goes in the high range if there's not enough low memory
>> and an additional buffer for swiotlb is allocated, hence the low 256M.
> I understand, but why 256M (as low) for arm64? x86_64 setups usually
> have more system memory available as compared to several commercially
> available arm64 setups. So is the intent, just to keep the behavior
> similar between arm64 and x86_64?
>
> Should we have a CONFIG option / bootarg to help one select the max
> 'low_size'? Currently the ' low_size' value is calculated as:
>
> /*
> * two parts from kernel/dma/swiotlb.c:
> * -swiotlb size: user-specified with swiotlb= or default.
> *
> * -swiotlb overflow buffer: now hardcoded to 32k. We round it
> * to 8M for other buffers that may need to stay low too. Also
> * make sure we allocate enough extra low memory so that we
> * don't run out of DMA buffers for 32-bit devices.
> */
> low_size = max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20);
>
> Since many arm64 boards ship with swiotlb=0 (turned off) via kernel
> bootargs, the low_size, still ends up being 256M in such cases,
> whereas this 256M can be used for some other purposes - so should we
> be limiting this to 64M and failing the crash kernel allocation
> request (gracefully) otherwise?
>
>> We could (as an additional patch), subtract the 256M from the high
>> allocation so that you'd get a low 256M and a high 512M, not sure it's
>> worth it. Note that with a "crashkernel=768M,high" option, you still get
>> the additional low 256M, otherwise the crashkernel won't be able to
>> boot as there's no memory in ZONE_DMA. In the explicit ",high" request
>> case, I'm not sure subtracted the 256M is more intuitive.
>> In 5.11, we also hope to fix the ZONE_DMA layout for non-RPi4 platforms
>> to cover the entire 32-bit address space (i.e. identical to the current
>> ZONE_DMA32).
>>
>>> IMO, we should test this feature more before including this in 5.11
>> Definitely. That's one of the reasons we haven't queued it yet. So any
>> help with testing here is appreciated.
> Sure, I am running more checks on this series. I will be soon back
> with more updates.
Sorry to bother you. I am looking forward to your review comments.
Thanks,
Chen Zhou
>
> Regards,
> Bhupesh
>
> .
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-10-19 2:45 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-07 13:47 [PATCH v12 0/9] support reserving crashkernel above 4G on arm64 kdump Chen Zhou
2020-09-07 13:47 ` [PATCH v12 1/9] x86: kdump: move CRASH_ALIGN to 2M Chen Zhou
2020-09-08 1:21 ` Dave Young
2020-09-08 3:19 ` chenzhou
2020-09-07 13:47 ` [PATCH v12 2/9] x86: kdump: make the lower bound of crash kernel reservation consistent Chen Zhou
2020-09-07 13:47 ` [PATCH v12 3/9] x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions reserve_crashkernel[_low]() Chen Zhou
2020-09-18 3:01 ` Dave Young
2020-09-18 3:57 ` chenzhou
2020-09-18 5:26 ` Dave Young
2020-09-18 7:25 ` Baoquan He
2020-09-18 8:59 ` chenzhou
2020-09-18 9:06 ` chenzhou
2020-10-05 17:20 ` Catalin Marinas
2020-09-07 13:47 ` [PATCH v12 4/9] x86: kdump: move reserve_crashkernel[_low]() into crash_core.c Chen Zhou
2020-09-07 13:47 ` [PATCH v12 5/9] arm64: kdump: introduce some macroes for crash kernel reservation Chen Zhou
2020-09-07 13:47 ` [PATCH v12 6/9] arm64: kdump: reimplement crashkernel=X Chen Zhou
2020-10-05 17:16 ` Catalin Marinas
2020-10-06 1:30 ` chenzhou
2020-09-07 13:47 ` [PATCH v12 7/9] kdump: add threshold for the required memory Chen Zhou
2020-10-05 17:12 ` Catalin Marinas
2020-10-06 1:34 ` chenzhou
2020-09-07 13:47 ` [PATCH v12 8/9] arm64: kdump: add memory for devices by DT property linux, usable-memory-range Chen Zhou
2020-09-07 13:47 ` [PATCH v12 9/9] kdump: update Documentation about crashkernel Chen Zhou
2020-10-05 17:19 ` Catalin Marinas
2020-10-06 2:10 ` chenzhou
2020-10-07 16:24 ` Catalin Marinas
2020-09-12 11:44 ` [PATCH v12 0/9] support reserving crashkernel above 4G on arm64 kdump John Donnelly
2020-10-05 17:09 ` Catalin Marinas
2020-10-05 17:42 ` Bhupesh Sharma
2020-10-06 1:48 ` chenzhou
2020-10-06 18:00 ` Catalin Marinas
2020-10-07 7:07 ` Bhupesh Sharma
2020-10-07 16:33 ` Catalin Marinas
2020-10-19 2:43 ` chenzhou [this message]
2020-09-15 7:16 ` chenzhou
2020-09-23 17:47 ` John Donnelly
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ab142d7d-55a7-eca6-4609-147e1605f02d@huawei.com \
--to=chenzhou10@huawei.com \
--cc=arnd@arndb.de \
--cc=bhe@redhat.com \
--cc=bhsharma@redhat.com \
--cc=catalin.marinas@arm.com \
--cc=corbet@lwn.net \
--cc=dyoung@redhat.com \
--cc=guohanjun@huawei.com \
--cc=horms@verge.net.au \
--cc=huawei.libin@huawei.com \
--cc=james.morse@arm.com \
--cc=john.p.donnelly@oracle.com \
--cc=kexec@lists.infradead.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=nsaenzjulienne@suse.de \
--cc=prabhakar.pkin@gmail.com \
--cc=robh+dt@kernel.org \
--cc=tglx@linutronix.de \
--cc=wangkefeng.wang@huawei.com \
--cc=will@kernel.org \
--cc=xiexiuqi@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).