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

[Yasuaki Ishimatsu]

2013/04/19 23:30, Toshi Kani wrote:
> On Fri, 2013-04-19 at 17:09 +0900, Yasuaki Ishimatsu wrote:
> > Hi Toshi,
> >
> > 2013/04/19 8:33, Yasuaki Ishimatsu wrote:
> > > 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.
> >
> > Oh, I missed "should be pointer of struct resource" part.
> > Please teach me your detailed idea. If this is defined as pointer,
> > how do we initialize this and manage bootmem resources?
> >
> > I'm thinking it but have no idea.

> Sure.  It's quite simple.  Since only bootmem_resource.sibling is used,
> it can be replaced with a pointer, such as bootmem_resource_free.  This
> avoids allocating a struct resource table as this code is supposed to
> save memory.
>
> So, first, declare the pointer below, which is initialized to NULL as
> BSS (checkpatch.pl complains if you set it to NULL explicitly).
>
>    static struct resource *bootmem_resource_free;
>
> Then, in free_resource(), this pointer replaces bootmem_resource.sibling
> as follows.
>
>    res->sibling = bootmem_resource_free;
>    bootmem_resource_free = res;
>
> Similarly, in get_resource().
>
>    if (bootmem_resource_free) {
>        res = bootmem_resource_free;
>        bootmem_resource_free = res->sibling;
>    }

Thank you for your detail explanation. I clearly understood your idea.
I'll update your comment and post a updated patch.

Thanks,
Yasuaki Ishimatsu

> Thanks,
> -Toshi


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