Re: [Patch 8/8] kexec: allow to shrink reserved memory

[Amerigo Wang]

Eric W. Biederman wrote:
> Amerigo Wang <amwang@xxxxxxxxxx> 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!


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/