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Date: Wed, 12 Aug 2009 20:11:55 -0700
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Amerigo Wang <amwang@...hat.com>
Cc: linux-kernel@...r.kernel.org, tony.luck@...el.com,
linux-ia64@...r.kernel.org, Neil Horman <nhorman@...hat.com>,
Andi Kleen <andi@...stfloor.org>, akpm@...ux-foundation.org,
bernhard.walle@....de, Fenghua Yu <fenghua.yu@...el.com>,
Ingo Molnar <mingo@...e.hu>,
Anton Vorontsov <avorontsov@...mvista.com>
Subject: Re: [Patch 8/8] kexec: allow to shrink reserved memory
Amerigo Wang <amwang@...hat.com> writes:
> This patch implements shrinking the reserved memory for crash kernel,
> if it is more than enough.
>
> For example, if you have already reserved 128M, now you just want 100M,
> you can do:
>
> # echo $((100*1024*1024)) > /sys/kernel/kexec_crash_size
Getting closer (comments inline)
Semantically this patch is non-contriversial and pretty
simple, but still needs a fair amount of review. Can
you put this patch at the front of your patch set.
> Signed-off-by: WANG Cong <amwang@...hat.com>
> Cc: Neil Horman <nhorman@...hat.com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Andi Kleen <andi@...stfloor.org>
>
> ---
>
> Index: linux-2.6/include/linux/kexec.h
> ===================================================================
> --- linux-2.6.orig/include/linux/kexec.h
> +++ linux-2.6/include/linux/kexec.h
> @@ -206,6 +206,9 @@ extern size_t vmcoreinfo_max_size;
>
> int __init parse_crashkernel(char *cmdline, unsigned long long system_ram,
> unsigned long long *crash_size, unsigned long long *crash_base);
> +int shrink_crash_memory(unsigned long new_size);
> +int kexec_crash_kernel_loaded(void);
> +size_t get_crash_memory_size(void);
>
> #else /* !CONFIG_KEXEC */
> struct pt_regs;
> Index: linux-2.6/kernel/kexec.c
> ===================================================================
> --- linux-2.6.orig/kernel/kexec.c
> +++ linux-2.6/kernel/kexec.c
> @@ -1083,6 +1083,76 @@ void crash_kexec(struct pt_regs *regs)
> }
> }
>
> +int kexec_crash_kernel_loaded(void)
> +{
> + int ret;
> + if (!mutex_trylock(&kexec_mutex))
> + return 1;
We don't need trylock on this code path
> + ret = kexec_crash_image != NULL;
> + mutex_unlock(&kexec_mutex);
> + return ret;
> +}
> +
> +size_t get_crash_memory_size(void)
> +{
> + size_t size;
> + if (!mutex_trylock(&kexec_mutex))
> + return 1;
We don't need trylock on this code path
> + size = crashk_res.end - crashk_res.start + 1;
> + mutex_unlock(&kexec_mutex);
> + return size;
> +}
> +
> +int shrink_crash_memory(unsigned long new_size)
> +{
> + struct page **pages;
> + int ret = 0;
> + int npages, i;
> + unsigned long addr;
> + unsigned long start, end;
> + void *vaddr;
> +
> + if (!mutex_trylock(&kexec_mutex))
> + return -EBUSY;
We don't need trylock on this code path
We are missing the check to see if the crash_kernel is loaded
under this lock instance. So I please move the kexec_crash_image != NULL
test inline here and kill the kexec_crash_kernel_loaded function.
> + start = crashk_res.start;
> + end = crashk_res.end;
> +
> + if (new_size >= end - start + 1) {
> + ret = -EINVAL;
> + if (new_size == end - start + 1)
> + ret = 0;
> + goto unlock;
> + }
> +
> + start = roundup(start, PAGE_SIZE);
> + end = roundup(start + new_size, PAGE_SIZE) - 1;
> + npages = (end + 1 - start ) / PAGE_SIZE;
> +
> + pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
> + if (!pages) {
> + ret = -ENOMEM;
> + goto unlock;
> + }
> + for (i = 0; i < npages; i++) {
> + addr = end + 1 + i * PAGE_SIZE;
> + pages[i] = virt_to_page(addr);
> + }
> +
> + vaddr = vm_map_ram(pages, npages, 0, PAGE_KERNEL);
This is the wrong kernel call to use. I expect this needs to look
like a memory hotplug event. This does not put the pages into the
free page pool.
> + if (!vaddr) {
> + ret = -ENOMEM;
> + goto free;
> + }
> + crashk_res.end = end;
> +
> +free:
> + kfree(pages);
> +unlock:
> + mutex_unlock(&kexec_mutex);
> + return ret;
> +}
> +
> static u32 *append_elf_note(u32 *buf, char *name, unsigned type, void *data,
> size_t data_len)
> {
> Index: linux-2.6/kernel/ksysfs.c
> ===================================================================
> --- linux-2.6.orig/kernel/ksysfs.c
> +++ linux-2.6/kernel/ksysfs.c
> @@ -100,6 +100,26 @@ static ssize_t kexec_crash_loaded_show(s
> }
> KERNEL_ATTR_RO(kexec_crash_loaded);
>
> +static ssize_t kexec_crash_size_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "%lu\n", get_crash_memory_size());
> +}
> +static ssize_t kexec_crash_size_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + unsigned long cnt;
> + int ret;
> +
> + if (kexec_crash_kernel_loaded())
> + return -ENOENT;
> + cnt = simple_strtoul(buf, NULL, 10);
> + ret = shrink_crash_memory(cnt);
> + return ret < 0 ? ret: count;
> +}
> +KERNEL_ATTR_RW(kexec_crash_size);
> +
> static ssize_t vmcoreinfo_show(struct kobject *kobj,
> struct kobj_attribute *attr, char *buf)
> {
> @@ -147,6 +167,7 @@ static struct attribute * kernel_attrs[]
> #ifdef CONFIG_KEXEC
> &kexec_loaded_attr.attr,
> &kexec_crash_loaded_attr.attr,
> + &kexec_crash_size_attr.attr,
> &vmcoreinfo_attr.attr,
> #endif
> NULL
--
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