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Date: Tue, 24 Oct 2017 14:06:11 +0800
From: Dave Young <dyoung@...hat.com>
To: Baoquan He <bhe@...hat.com>
Cc: kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, vgoyal@...hat.com, yinghai@...nel.org,
corbet@....net
Subject: Re: [PATCH 1/3] kdump: extend crashkernel=range:size to dynamically
increase reservation size
Hi Baoquan,
On 10/24/17 at 02:00pm, Baoquan He wrote:
> On 10/24/17 at 01:31pm, Dave Young wrote:
> > crashkernel=range:size syntax allows to reserve specified size for system
> > with total memory fall into the specified range. For example:
> > crashkernel=2G-3G:128M,3G-:256M reserves 128M for system with memory >=2G
> > and memory <3G, and reserves 256M for system with memory >= 3G
> >
> > In the above case 256M as a fixed value which can not fulfill very huge
> > systems with large memory and IO devices. As memory size increases usually
> > minimum memory requirement for booting will also increase. It is nearly
> > impossible for a kernel to run with a fixed limited memory size for all
> > kinds of systems.
> >
> > Thus extend the crashkernel=range:size to let user specify the scaling
> > ratio in kernel cmdline like below:
> > crashkernel=range:size^order, for example:
> > crashkernel=2G-:128M^14 reserve 128M + (total_memory - 128M) >> 14
> > for machines with over 2G memory.
>
> Well, ah.., this look a little ugly and tricky. Leave this to other
> reviewers to comment.
But this is better than embed policy in kernel.. RHEL takes a
crashkernel=auto which do the scaling. Leaving user to determine
the scaling ratio is the better way.
OTOH, this is an improvement to current crashkernel=range:size
which can not scale the size before.
>
> >
> > Also s/start-[end]/[start]-end/ in kernel-parameters.txt according to code
> >
> > Signed-off-by: Dave Young <dyoung@...hat.com>
> > ---
> > Documentation/admin-guide/kernel-parameters.txt | 10 ++++--
> > Documentation/kdump/kdump.txt | 7 ++--
> > kernel/crash_core.c | 35 +++++++++++++++++++++---
> > 3 files changed, 41 insertions(+), 11 deletions(-)
> >
> > --- linux-x86.orig/kernel/crash_core.c
> > +++ linux-x86/kernel/crash_core.c
> > @@ -31,7 +31,7 @@ static unsigned char *vmcoreinfo_data_sa
> > /*
> > * This function parses command lines in the format
> > *
> > - * crashkernel=ramsize-range:size[,...][@offset]
> > + * crashkernel=ramsize-range:size[,...][@offset][^order]
> > *
> > * The function returns 0 on success and -EINVAL on failure.
> > */
> > @@ -41,6 +41,7 @@ static int __init parse_crashkernel_mem(
> > unsigned long long *crash_base)
> > {
> > char *cur = cmdline, *tmp;
> > + bool infinite_end = false;
> >
> > /* for each entry of the comma-separated list */
> > do {
> > @@ -93,13 +94,21 @@ static int __init parse_crashkernel_mem(
> > /* match ? */
> > if (system_ram >= start && system_ram < end) {
> > *crash_size = size;
> > + if (end == ULLONG_MAX)
> > + infinite_end = true;
> > break;
> > }
> > } while (*cur++ == ',');
> >
> > - if (*crash_size > 0) {
> > - while (*cur && *cur != ' ' && *cur != '@')
> > + if (*crash_size <= 0)
> > + goto out;
> > +
> > + while (*cur && *cur != ' ') {
> > + if (*cur != '@' && *cur != '^') {
> > cur++;
> > + continue;
> > + }
> > +
> > if (*cur == '@') {
> > cur++;
> > *crash_base = memparse(cur, &tmp);
> > @@ -107,10 +116,28 @@ static int __init parse_crashkernel_mem(
> > pr_warn("Memory value expected after '@'\n");
> > return -EINVAL;
> > }
> > - }
> > + cur = tmp;
> > + } else if (*cur == '^' && infinite_end ) {
> > + unsigned long long shift, size;
> > +
> > + cur++;
> > + shift = memparse(cur, &tmp);
> > + if (cur == tmp) {
> > + pr_warn("Memory reservation scale order expected after '^'\n");
> > + return -EINVAL;
> > + }
> > + size = (system_ram - *crash_size) >> shift;
> > + size = *crash_size + roundup(size, 1ULL << 20);
> > + if (size < system_ram)
> > + *crash_size = size;
> > + cur = tmp;
> > + } else
> > + cur++;
> > }
> >
> > return 0;
> > +out:
> > + return -EINVAL;
> > }
> >
> > /*
> > --- linux-x86.orig/Documentation/admin-guide/kernel-parameters.txt
> > +++ linux-x86/Documentation/admin-guide/kernel-parameters.txt
> > @@ -680,12 +680,14 @@
> > is selected automatically. Check
> > Documentation/kdump/kdump.txt for further details.
> >
> > - crashkernel=range1:size1[,range2:size2,...][@offset]
> > + crashkernel=range1:size1[,range2:size2,...][@offset][^order]
> > [KNL] Same as above, but depends on the memory
> > in the running system. The syntax of range is
> > - start-[end] where start and end are both
> > - a memory unit (amount[KMG]). See also
> > - Documentation/kdump/kdump.txt for an example.
> > + [start]-end where start and end are both
> > + a memory unit (amount[KMG]). In case the end of the
> > + range is infinity '^order' can be used to scale
> > + the size to size + (total_mem - start) >> 2^order
> > + See also Documentation/kdump/kdump.txt for an example.
> >
> > crashkernel=size[KMG],high
> > [KNL, x86_64] range could be above 4G. Allow kernel
> > --- linux-x86.orig/Documentation/kdump/kdump.txt
> > +++ linux-x86/Documentation/kdump/kdump.txt
> > @@ -267,19 +267,20 @@ been removed from the machine.
> >
> > The syntax is:
> >
> > - crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
> > + crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset][^order]
> > range=start-[end]
> >
> > For example:
> >
> > - crashkernel=512M-2G:64M,2G-:128M
> > + crashkernel=512M-2G:64M,2G-:128M^14
> >
> > This would mean:
> >
> > 1) if the RAM is smaller than 512M, then don't reserve anything
> > (this is the "rescue" case)
> > 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
> > - 3) if the RAM size is larger than 2G, then reserve 128M
> > + 3) if the RAM size is larger than 2G, then reserve:
> > + 128M + (total_mem - 128M) >> 14
> >
> >
> >
> >
> >
Thanks
Dave
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