linux-kernel - Re: [Bug fix PATCH v4] Reusing a resource structure allocated by bootmem

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Message-ID: <1366295000.3824.47.camel@misato.fc.hp.com>
Date:	Thu, 18 Apr 2013 08:23:20 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, linuxram@...ibm.com,
	rientjes@...gle.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [Bug fix PATCH v4] Reusing a resource structure allocated by
 bootmem

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;

> +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.

> +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);
}

Thanks,
-Toshi

> +
> +	if (!res)
> +		res = kzalloc(sizeof(struct resource), flags);
> +
> +	return res;
> +}
> +


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