Re: [Bug fix PATCH v4] Reusing a resource structure allocated bybootmem

[Yasuaki Ishimatsu]

Hi Toshi,

2013/04/18 23:23, Toshi Kani wrote:
> On Thu, 2013-04-18 at 17:36 +0900, Yasuaki Ishimatsu wrote:
> > When hot removing memory presented at boot time, following messages are shown:
>   :
> > diff --git a/kernel/resource.c b/kernel/resource.c
> > index 4aef886..637e8d2 100644
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -21,6 +21,7 @@
> >   #include <linux/seq_file.h>
> >   #include <linux/device.h>
> >   #include <linux/pfn.h>
> > +#include <linux/mm.h>
> >   #include <asm/io.h>
> >
> >
> > @@ -50,6 +51,16 @@ struct resource_constraint {
> >
> >   static DEFINE_RWLOCK(resource_lock);
> >
> > +/*
> > + * For memory hotplug, there is no way to free resource entries allocated
> > + * by boot mem after the system is up. So for reusing the resource entry
> > + * we need to remember the resource.
> > + */
> > +struct resource bootmem_resource = {
> > +	.sibling = NULL,
> > +};

> This should be a pointer of struct resource and declared as static, such
> as:
>
> static struct resource *bootmem_resource_free;

O.K. I'll update it.

> > +static DEFINE_SPINLOCK(bootmem_resource_lock);
> > +
> >   static void *r_next(struct seq_file *m, void *v, loff_t *pos)
> >   {
> >   	struct resource *p = v;
> > @@ -151,6 +162,39 @@ __initcall(ioresources_init);
> >
> >   #endif /* CONFIG_PROC_FS */
> >
> > +static void free_resource(struct resource *res)
> > +{
> > +	if (!res)
> > +		return;
> > +
> > +	if (PageSlab(virt_to_head_page(res))) {
> > +		spin_lock(&bootmem_resource_lock);
> > +		res->sibling = bootmem_resource.sibling;
> > +		bootmem_resource.sibling = res;
> > +		spin_unlock(&bootmem_resource_lock);
> > +	} else {
> > +		kfree(res);
> > +	}
> > +}

> I second with Johannes.

I'll update it.

> > +static struct resource *get_resource(gfp_t flags)
> > +{
> > +	struct resource *res = NULL;
> > +
> > +	spin_lock(&bootmem_resource_lock);
> > +	if (bootmem_resource.sibling) {
> > +		res = bootmem_resource.sibling;
> > +		bootmem_resource.sibling = res->sibling;
> > +		memset(res, 0, sizeof(struct resource));
> > +	}
> > +	spin_unlock(&bootmem_resource_lock);

> I prefer to keep memset() outside of the spin lock.
>
> spin_lock(&bootmem_resource_lock);
> if (..) {
> 	:
> 	spin_unlock(&bootmem_resource_lock);
> 	memset(res, 0, sizeof(struct resource));
> } else {
> 	spin_unlock(&bootmem_resource_lock);
> 	res = kzalloc(sizeof(struct resource), flags);
> }

Hmm. It is a little ugly. How about it?

spin_lock(&bootmem_resource_lock);
if (bootmem_resource.sibling) {
	res = bootmem_resource.sibling;
	bootmem_resource.sibling = res->sibling;
}
spin_unlock(&bootmem_resource_lock);

if (res)
	memset(res, 0, sizeof(struct resource));
else	
	res = kzalloc(sizeof(struct resource), flags);

Thanks,
Yasuaki Ishimatsu

> Thanks,
> -Toshi
>
> > +
> > +
> > +	return res;
> > +}
> > +


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