On Wed, 24 Apr 2013 08:50:21 +0900 Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> wrote:
> When hot removing memory presented at boot time, following messages are shown:
>
> [ 296.867031] ------------[ cut here ]------------
> [ 296.922273] kernel BUG at mm/slub.c:3409!
>
> ...
>
> The reason why the messages are shown is to release a resource structure,
> allocated by bootmem, by kfree(). So when we release a resource structure,
> we should check whether it is allocated by bootmem or not.
>
> But even if we know a resource structure is allocated by bootmem, we cannot
> release it since SLxB cannot treat it. So for reusing a resource structure,
> this patch remembers it by using bootmem_resource as follows:
>
> When releasing a resource structure by free_resource(), free_resource() checks
> whether the resource structure is allocated by bootmem or not. If it is
> allocated by bootmem, free_resource() adds it to bootmem_resource. If it is
> not allocated by bootmem, free_resource() release it by kfree().
>
> And when getting a new resource structure by get_resource(), get_resource()
> checks whether bootmem_resource has released resource structures or not. If
> there is a released resource structure, get_resource() returns it. If there is
> not a releaed resource structure, get_resource() returns new resource structure
> allocated by kzalloc().
>
> ...
>
Looks good to me.
> --- 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 +51,14 @@ 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.
> + */
> +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 +160,40 @@ __initcall(ioresources_init);
>
> #endif /* CONFIG_PROC_FS */
>
> +static void free_resource(struct resource *res)
> +{
> + if (!res)
> + return;
> +
> + if (!PageSlab(virt_to_head_page(res))) {
Did you consider using a bit in resource.flags? There appear to be
four free ones left. The VM trickery will work OK I guess, but isn't
very "nice".
> + spin_lock(&bootmem_resource_lock);
> + res->sibling = bootmem_resource_free;
> + bootmem_resource_free = res;
> + spin_unlock(&bootmem_resource_lock);
> + } else {
> + kfree(res);
> + }
> +}
> +
> +static struct resource *get_resource(gfp_t flags)
> +{
> + struct resource *res = NULL;
> +
> + spin_lock(&bootmem_resource_lock);
> + if (bootmem_resource_free) {
> + res = bootmem_resource_free;
> + bootmem_resource_free = res->sibling;
> + }
> + spin_unlock(&bootmem_resource_lock);
> +
> + if (res)
> + memset(res, 0, sizeof(struct resource));
> + else
> + res = kzalloc(sizeof(struct resource), flags);
> +
> + return res;
> +}
I think I'll rename this to alloc_resource(). In Linux "get" often
(but not always) means "take a reference on". So "get" pairs with
"put" and "alloc" pairs with "free".
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