Linux-Doc Archive on lore.kernel.org
 help / color / Atom feed
From: Chen Zhou <chenzhou10@huawei.com>
To: <catalin.marinas@arm.com>, <will@kernel.org>,
	<james.morse@arm.com>, <tglx@linutronix.de>, <mingo@redhat.com>,
	<dyoung@redhat.com>, <bhe@redhat.com>, <corbet@lwn.net>,
	<John.P.donnelly@oracle.com>, <prabhakar.pkin@gmail.com>,
	<bhsharma@redhat.com>
Cc: <horms@verge.net.au>, <robh+dt@kernel.org>, <arnd@arndb.de>,
	<nsaenzjulienne@suse.de>, <linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <kexec@lists.infradead.org>,
	<linux-doc@vger.kernel.org>, <chenzhou10@huawei.com>,
	<guohanjun@huawei.com>, <xiexiuqi@huawei.com>,
	<huawei.libin@huawei.com>, <wangkefeng.wang@huawei.com>
Subject: [PATCH v11 5/5] kdump: update Documentation about crashkernel
Date: Sat, 1 Aug 2020 21:08:56 +0800
Message-ID: <20200801130856.86625-6-chenzhou10@huawei.com> (raw)
In-Reply-To: <20200801130856.86625-1-chenzhou10@huawei.com>

Now the behavior of crashkernel=X has been changed, which tries low
allocation in ZONE_DMA, and fall back to high allocation if it fails.

If requized size X is too large and leads to very little free memory
in ZONE_DMA after low allocation, the system may not work well.
So add a threshold and go for high allocation directly if the required
size is too large. The threshold is set as the half of low memory.

If crash_base is outside ZONE_DMA, try to allocate at least 256M in
ZONE_DMA automatically. "crashkernel=Y,low" can be used to allocate
specified size low memory. For non-RPi4 platforms, change ZONE_DMA
memtioned above to ZONE_DMA32.

So update the Documentation.

Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
---
 Documentation/admin-guide/kdump/kdump.rst     | 21 ++++++++++++++++---
 .../admin-guide/kernel-parameters.txt         | 11 ++++++++--
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index 2da65fef2a1c..4b58f97351d5 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -299,7 +299,15 @@ Boot into System Kernel
    "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
    starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
 
-   On x86 and x86_64, use "crashkernel=64M@16M".
+   On x86 use "crashkernel=64M@16M".
+
+   On x86_64, use "crashkernel=X" to select a region under 4G first, and
+   fall back to reserve region above 4G.
+   We can also use "crashkernel=X,high" to select a region above 4G, which
+   also tries to allocate at least 256M below 4G automatically and
+   "crashkernel=Y,low" can be used to allocate specified size low memory.
+   Use "crashkernel=Y@X" if you really have to reserve memory from specified
+   start address X.
 
    On ppc64, use "crashkernel=128M@32M".
 
@@ -316,8 +324,15 @@ Boot into System Kernel
    kernel will automatically locate the crash kernel image within the
    first 512MB of RAM if X is not given.
 
-   On arm64, use "crashkernel=Y[@X]".  Note that the start address of
-   the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
+   On arm64, use "crashkernel=X" to try low allocation in ZONE_DMA, and
+   fall back to high allocation if it fails. And go for high allocation
+   directly if the required size is too large. If crash_base is outside
+   ZONE_DMA, try to allocate at least 256M in ZONE_DMA automatically.
+   "crashkernel=Y,low" can be used to allocate specified size low memory.
+   For non-RPi4 platforms, change ZONE_DMA memtioned above to ZONE_DMA32.
+   Use "crashkernel=Y@X" if you really have to reserve memory from
+   specified start address X. Note that the start address of the kernel,
+   X if explicitly specified, must be aligned to 2MiB (0x200000).
 
 Load the Dump-capture Kernel
 ============================
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fb95fad81c79..d1b6016850d6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -722,6 +722,10 @@
 			[KNL, x86_64] select a region under 4G first, and
 			fall back to reserve region above 4G when '@offset'
 			hasn't been specified.
+			[KNL, arm64] Try low allocation in ZONE_DMA, fall back
+			to high allocation if it fails when '@offset' hasn't been
+			specified. For non-RPi4 platforms, change ZONE_DMA to
+			ZONE_DMA32.
 			See Documentation/admin-guide/kdump/kdump.rst for further details.
 
 	crashkernel=range1:size1[,range2:size2,...][@offset]
@@ -746,13 +750,16 @@
 			requires at least 64M+32K low memory, also enough extra
 			low memory is needed to make sure DMA buffers for 32-bit
 			devices won't run out. Kernel would try to allocate at
-			at least 256M below 4G automatically.
+			least 256M below 4G automatically.
 			This one let user to specify own low range under 4G
 			for second kernel instead.
 			0: to disable low allocation.
 			It will be ignored when crashkernel=X,high is not used
 			or memory reserved is below 4G.
-
+			[KNL, arm64] range under 4G.
+			This one let user to specify a low range in ZONE_DMA for
+			crash dump kernel. For non-RPi4 platforms, change ZONE_DMA
+			to ZONE_DMA32.
 	cryptomgr.notests
 			[KNL] Disable crypto self-tests
 
-- 
2.20.1


  parent reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-01 13:08 [PATCH v11 0/5] support reserving crashkernel above 4G on arm64 kdump Chen Zhou
2020-08-01 13:08 ` [PATCH v11 1/5] arm64: kdump: add macro CRASH_ALIGN and CRASH_ADDR_LOW_MAX Chen Zhou
2020-08-01 13:08 ` [PATCH v11 2/5] x86: kdump: move reserve_crashkernel_low() into crash_core.c Chen Zhou
2020-08-06 13:36   ` Ingo Molnar
2020-08-08  9:59   ` Dave Young
2020-08-01 13:08 ` [PATCH v11 3/5] arm64: kdump: reimplement crashkernel=X Chen Zhou
2020-08-01 13:08 ` [PATCH v11 4/5] arm64: kdump: add memory for devices by DT property linux,usable-memory-range Chen Zhou
2020-08-01 13:08 ` Chen Zhou [this message]
2020-08-08 10:02   ` [PATCH v11 5/5] kdump: update Documentation about crashkernel Dave Young
2020-08-06 11:37 ` [PATCH v11 0/5] support reserving crashkernel above 4G on arm64 kdump Dave Young

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=20200801130856.86625-6-chenzhou10@huawei.com \
    --to=chenzhou10@huawei.com \
    --cc=John.P.donnelly@oracle.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=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

Linux-Doc Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-doc/0 linux-doc/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-doc linux-doc/ https://lore.kernel.org/linux-doc \
		linux-doc@vger.kernel.org
	public-inbox-index linux-doc

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-doc


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git