From: Catalin Marinas <catalin.marinas@arm.com>
To: Bhupesh Sharma <bhsharma@redhat.com>
Cc: John Donnelly <john.p.donnelly@oracle.com>,
Chen Zhou <chenzhou10@huawei.com>, Will Deacon <will@kernel.org>,
James Morse <james.morse@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, RuiRui Yang <dyoung@redhat.com>,
Baoquan He <bhe@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
Prabhakar Kushwaha <prabhakar.pkin@gmail.com>,
Simon Horman <horms@verge.net.au>,
Rob Herring <robh+dt@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
nsaenzjulienne@suse.de,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
kexec mailing list <kexec@lists.infradead.org>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>,
guohanjun@huawei.com, xiexiuqi@huawei.com,
huawei.libin@huawei.com, wangkefeng.wang@huawei.com
Subject: Re: [PATCH v12 0/9] support reserving crashkernel above 4G on arm64 kdump
Date: Wed, 7 Oct 2020 17:33:19 +0100 [thread overview]
Message-ID: <20201007163319.GS3462@gaia> (raw)
In-Reply-To: <CACi5LpMmccLX9p0ZXnEbWHgn2LRrVSDQZF9zBGzfZySe3TvXEQ@mail.gmail.com>
On Wed, Oct 07, 2020 at 12:37:49PM +0530, Bhupesh Sharma wrote:
> 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?
Similar in the sense of the fallback to high memory and some low memory
allocation but the amounts can vary per architecture.
> 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?
I think it makes sense to set a low_size = 0 if
swiotlb_size_or_default() is 0. The assumption would be that if the main
kernel doesn't need an swiotlb, the crashdump one wouldn't need it
either. But this probably needs the ZONE_DMA for non-RPi4 platforms
addressed as well (expanded to the whole ZONE_DMA32).
--
Catalin
next prev parent reply other threads:[~2020-10-07 16:33 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 [this message]
2020-10-19 2:43 ` chenzhou
2020-09-15 7:16 ` chenzhou
2020-09-23 17:47 ` John Donnelly
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