Date:	Mon, 17 Dec 2012 10:02:31 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
Cc:	kexec@...ts.infradead.org, ebiederm@...ssion.com,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] Add the values related to buddy system for filtering
 free pages.

CCing Andrew Morton. I think he picks kexec patches.



On Mon, Dec 10, 2012 at 08:17:05AM -0500, Vivek Goyal wrote:
> On Mon, Dec 10, 2012 at 10:39:13AM +0900, Atsushi Kumagai wrote:
> > This patch adds the values related to buddy system to vmcoreinfo data
> > so that makedumpfile (dump filtering command) can filter out all free
> > pages with the new logic.
> > It's faster than the current logic because it can distinguish free page
> > by analyzing page structure at the same time as filtering for other
> > unnecessary pages (e.g. anonymous page).
> > OTOH, the current logic has to trace free_list to distinguish free 
> > pages while analyzing page structure to filter out other unnecessary
> > pages.
> > 
> > The new logic uses the fact that buddy page is marked by _mapcount == 
> > PAGE_BUDDY_MAPCOUNT_VALUE. But, _mapcount shares its memory with other
> > fields for SLAB/SLUB when PG_slab is set, so we need to check if PG_slab
> > is set or not before looking up _mapcount value.
> > And we can get the order of buddy system from private field.
> > To sum it up, the values below are required for this logic.
> > 
> > Required values:
> >   - OFFSET(page._mapcount)
> >   - OFFSET(page.private)
> >   - NUMBER(PG_slab)
> >   - NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE)
> > 
> > Changelog from v1 to v2:
> > 1. remove SIZE(pageflags)
> >   The new logic was changed after I sent v1 patch.  
> >   Accordingly, SIZE(pageflags) has been unnecessary for makedumpfile.
> > 
> > What's makedumpfile:
> >   makedumpfile creates a small dumpfile by excluding unnecessary pages
> >   for the analysis. To distinguish unnecessary pages, makedumpfile gets
> >   the vmcoreinfo data which has the minimum debugging information only
> >   for dump filtering.
> > 
> > Signed-off-by: Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
> 
> Looks good to me.
> 
> Acked-by: Vivek Goyal <vgoyal@...hat.com>
> 
> Thanks
> Vivek
> 
> > ---
> >  kernel/kexec.c |    4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/kernel/kexec.c b/kernel/kexec.c
> > index 5e4bd78..b27efe4 100644
> > --- a/kernel/kexec.c
> > +++ b/kernel/kexec.c
> > @@ -1490,6 +1490,8 @@ static int __init crash_save_vmcoreinfo_init(void)
> > 	VMCOREINFO_OFFSET(page, _count);
> > 	VMCOREINFO_OFFSET(page, mapping);
> > 	VMCOREINFO_OFFSET(page, lru);
> > +	VMCOREINFO_OFFSET(page, _mapcount);
> > +	VMCOREINFO_OFFSET(page, private);
> > 	VMCOREINFO_OFFSET(pglist_data, node_zones);
> > 	VMCOREINFO_OFFSET(pglist_data, nr_zones);
> >  #ifdef CONFIG_FLAT_NODE_MEM_MAP
> > @@ -1512,6 +1514,8 @@ static int __init crash_save_vmcoreinfo_init(void)
> > 	VMCOREINFO_NUMBER(PG_lru);
> > 	VMCOREINFO_NUMBER(PG_private);
> > 	VMCOREINFO_NUMBER(PG_swapcache);
> > +	VMCOREINFO_NUMBER(PG_slab);
> > +	VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
> > 
> > 	arch_crash_save_vmcoreinfo();
> > 	update_vmcoreinfo_note();
> > --
> > 1.7.9.2
> > 
> > _______________________________________________
> > kexec mailing list
> > kexec@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> 
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
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