lkml.org 
[lkml]   [2009]   [Aug]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Patch 8/8] kexec: allow to shrink reserved memory
Eric W. Biederman wrote:
> Amerigo Wang <amwang@redhat.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.
>
>

Sure, I will do it when I resend them next time.

I add mm people into Cc.
>> 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
>

OK.

>
>> + 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
>
>

Hmm, crashk_res is a global struct, so other process can also
change it... but currently no process does that, right?

>> + 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.
>

Ok, no problem.

>
>> + 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.
>

Well, I also wanted to use an memory-hotplug API, but that will make the
code depend on memory-hotplug, which certainly is not what we want...

I checked the mm code, actually what I need is an API which is similar
to add_active_range(), but add_active_range() can't be used here since
it is marked as "__init".

Do we have that kind of API in mm? I can't find one.

Thanks!




\
 
 \ /
  Last update: 2009-08-13 05:33    [from the cache]
©2003-2011 Jasper Spaans