Hello Vivek, On Fri, 7 Dec 2012 10:08:05 -0500 Vivek Goyal <vgoyal at redhat.com> wrote: > On Wed, Nov 21, 2012 at 05:02:47PM +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. The values below are required to distinguish > > it. > > > > Required values: > > - OFFSET(page._mapcount) > > - OFFSET(page.private) > > - SIZE(pageflags) > > - NUMBER(PG_slab) > > - NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE) > > > > As per your explanation, you should just need to export page._mapcount > offset and PAGE_BUDDY_MAPCOUNT_VALUE value so that you can figure out > if a page is free or not. > > Why do we need rest of the three fields. > > - OFFSET(page.private) > - SIZE(pageflags) > - NUMBER(PG_slab) Thanks for your comment. SIZE(pageflags) is unnecessary as you said, but the other two are certainly necessary. I modified the description in v2 to make it clear, please see below: https://lkml.org/lkml/2012/12/9/138 Thanks Atsushi Kumagai
