Messages in this thread | | | Date | Fri, 26 Apr 2013 10:57:38 +0900 | From | Yasuaki Ishimatsu <> | Subject | Re: [Resend][Bug fix PATCH v5] Reusing a resource structure allocated by bootmem |
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2013/04/25 5:37, Andrew Morton wrote: > On Wed, 24 Apr 2013 08:50:21 +0900 Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> 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".
I forgot to answer it. I think so too. And I have no objection about your update patch.
Thanks, Yasuaki Ishimatsu
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