From: Baoquan He <bhe@redhat•com>
To: Michal Hocko <mhocko@kernel•org>
Cc: Andrew Morton <akpm@linux-foundation•org>,
linux-kernel@vger•kernel.org, robh+dt@kernel•org,
dan.j.williams@intel•com, nicolas.pitre@linaro•org,
josh@joshtriplett•org, fengguang.wu@intel•com, bp@suse•de,
andy.shevchenko@gmail•com, patrik.r.jakobsson@gmail•com,
airlied@linux•ie, kys@microsoft•com, haiyangz@microsoft•com,
sthemmin@microsoft•com, dmitry.torokhov@gmail•com,
frowand.list@gmail•com, keith.busch@intel•com,
jonathan.derrick@intel•com, lorenzo.pieralisi@arm•com,
bhelgaas@google•com, tglx@linutronix•de, brijesh.singh@amd•com,
jglisse@redhat•com, thomas.lendacky@amd•com,
gregkh@linuxfoundation•org, baiyaowei@cmss•chinamobile.com,
richard.weiyang@gmail•com, devel@linuxdriverproject•org,
linux-input@vger•kernel.org, linux-nvdimm@lists•01.org,
devicetree@vger•kernel.org, linux-pci@vger•kernel.org,
ebiederm@xmission•com, vgoyal@redhat•com, dyoung@redhat•com,
yinghai@kernel•org, monstr@monstr•eu, davem@davemloft•net,
chris@zankel•net, jcmvbkbc@gmail•com, gustavo@padovan•org,
maarten.lankhorst@linux•intel.com, seanpaul@chromium•org,
linux-parisc@vger•kernel.org, linuxppc-dev@lists•ozlabs.org,
kexec@lists•infradead.org
Subject: Re: [PATCH v7 4/4] kexec_file: Load kernel at top of system RAM if required
Date: Wed, 25 Jul 2018 14:48:13 +0800 [thread overview]
Message-ID: <20180725064813.GI6480@MiWiFi-R3L-srv> (raw)
In-Reply-To: <20180723143443.GD18181@dhcp22.suse.cz>
On 07/23/18 at 04:34pm, Michal Hocko wrote:
> On Thu 19-07-18 23:17:53, Baoquan He wrote:
> > Kexec has been a formal feature in our distro, and customers owning
> > those kind of very large machine can make use of this feature to speed
> > up the reboot process. On uefi machine, the kexec_file loading will
> > search place to put kernel under 4G from top to down. As we know, the
> > 1st 4G space is DMA32 ZONE, dma, pci mmcfg, bios etc all try to consume
> > it. It may have possibility to not be able to find a usable space for
> > kernel/initrd. From the top down of the whole memory space, we don't
> > have this worry.
>
> I do not have the full context here but let me note that you should be
> careful when doing top-down reservation because you can easily get into
> hotplugable memory and break the hotremove usecase. We even warn when
> this is done. See memblock_find_in_range_node
Kexec read kernel/initrd file into buffer, just search usable positions
for them to do the later copying. You can see below struct kexec_segment,
for the old kexec_load, kernel/initrd are read into user space buffer,
the @buf stores the user space buffer address, @mem stores the position
where kernel/initrd will be put. In kernel, it calls
kimage_load_normal_segment() to copy user space buffer to intermediate
pages which are allocated with flag GFP_KERNEL. These intermediate pages
are recorded as entries, later when user execute "kexec -e" to trigger
kexec jumping, it will do the final copying from the intermediate pages
to the real destination pages which @mem pointed. Because we can't touch
the existed data in 1st kernel when do kexec kernel loading. With my
understanding, GFP_KERNEL will make those intermediate pages be
allocated inside immovable area, it won't impact hotplugging. But the
@mem we searched in the whole system RAM might be lost along with
hotplug. Hence we need do kexec kernel again when hotplug event is
detected.
#define KEXEC_CONTROL_MEMORY_GFP (GFP_KERNEL | __GFP_NORETRY)
struct kexec_segment {
/*
* This pointer can point to user memory if kexec_load() system
* call is used or will point to kernel memory if
* kexec_file_load() system call is used.
*
* Use ->buf when expecting to deal with user memory and use ->kbuf
* when expecting to deal with kernel memory.
*/
union {
void __user *buf;
void *kbuf;
};
size_t bufsz;
unsigned long mem;
size_t memsz;
};
Thanks
Baoquan
next prev parent reply other threads:[~2018-07-25 6:48 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-18 2:49 [PATCH v7 0/4] resource: Use list_head to link sibling resource Baoquan He
2018-07-18 2:49 ` [PATCH v7 1/4] resource: Move reparent_resources() to kernel/resource.c and make it public Baoquan He
2018-07-18 16:36 ` Andy Shevchenko
2018-07-18 16:37 ` Andy Shevchenko
2018-07-19 15:18 ` Baoquan He
2018-07-18 2:49 ` [PATCH v7 2/4] resource: Use list_head to link sibling resource Baoquan He
2018-07-18 2:49 ` [PATCH v7 3/4] resource: add walk_system_ram_res_rev() Baoquan He
2018-07-18 2:49 ` [PATCH v7 4/4] kexec_file: Load kernel at top of system RAM if required Baoquan He
2018-07-18 22:33 ` Andrew Morton
2018-07-19 15:17 ` Baoquan He
2018-07-19 19:44 ` Andrew Morton
2018-07-25 2:21 ` Baoquan He
2018-07-23 14:34 ` Michal Hocko
2018-07-25 6:48 ` Baoquan He [this message]
2018-07-26 12:59 ` Michal Hocko
2018-07-26 13:09 ` Baoquan He
2018-07-26 13:12 ` Michal Hocko
2018-07-26 13:14 ` Michal Hocko
2018-07-26 13:37 ` Baoquan He
2018-07-26 14:01 ` Michal Hocko
2018-07-26 15:10 ` Baoquan He
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