Re: [Patch 8/8] kexec: allow to shrink reserved memory

[Amerigo Wang]

KAMEZAWA Hiroyuki wrote:
> On Mon, 17 Aug 2009 17:50:21 +0800
> Amerigo Wang <amwang@xxxxxxxxxx> wrote:
>
>   
> > Eric W. Biederman wrote:
> >     
> > > Amerigo Wang <amwang@xxxxxxxxxx> writes:
> > >
> > >   
> > >       
> > > > Not that simple, marking it as "__init" means it uses some "__init" data which
> > > > will be dropped after initialization.
> > > >     
> > > >         
> > > If we start with the assumption that we will be reserving to much and
> > > will free the memory once we know how much we really need I see a very
> > > simple way to go about this. We ensure that the reservation of crash
> > > kernel memory is done through a normal allocation so that we have
> > > struct page entries for every page.  On 32bit x86 that is an extra 1MB
> > > for a 128MB allocation.
> > >
> > > Then when it comes time to release that memory we clear whatever magic
> > > flags we have on the page (like PG_reserve) and call free_page.
> > >   
> > >       
> > Hmm, my MM knowledge is not good enough to judge if this works...
> > I need to check more MM source code.
> >
> > Can any MM people help?
> >
> >     
> Hm, memory-hotplug guy is here.
>   

Hi, thank you!
> Can I have a question ?
>
>   - How crash kernel's memory is preserved at boot ?
>   

Use bootmem, I think.

>     It's hidden from the system before mem_init() ?
>   

Not sure, but probably yes. It is reserved in setup_arch() which is 
before mm_init() which calls mem_init().

Do you have any advice to free that reserved memory after boot? :)

Thanks.



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