Re: [PATCH 0/3] makedumpfile: hugepage filtering for vmcore dump

[HATAYAMA Daisuke]

(2013/11/07 9:54), HATAYAMA Daisuke wrote:
> (2013/11/06 11:21), Atsushi Kumagai wrote:
> > (2013/11/06 5:27), Vivek Goyal wrote:
> > > On Tue, Nov 05, 2013 at 09:45:32PM +0800, Jingbai Ma wrote:
> > > > This patch set intend to exclude unnecessary hugepages from vmcore dump file.
> > > >
> > > > This patch requires the kernel patch to export necessary data structures into
> > > > vmcore: "kexec: export hugepage data structure into vmcoreinfo"
> > > > http://lists.infradead.org/pipermail/kexec/2013-November/009997.html
> > > >
> > > > This patch introduce two new dump levels 32 and 64 to exclude all unused and
> > > > active hugepages. The level to exclude all unnecessary pages will be 127 now.
> > >
> > > Interesting. Why hugepages should be treated any differentely than normal
> > > pages?
> > >
> > > If user asked to filter out free page, then it should be filtered and
> > > it should not matter whether it is a huge page or not?
> >
> > I'm making a RFC patch of hugepages filtering based on such policy.
> >
> > I attach the prototype version.
> > It's able to filter out also THPs, and suitable for cyclic processing
> > because it depends on mem_map and looking up it can be divided into
> > cycles. This is the same idea as page_is_buddy().
> >
> > So I think it's better.
>
> > @@ -4506,14 +4583,49 @@ __exclude_unnecessary_pages(unsigned long mem_map,
> >                && !isAnon(mapping)) {
> >                if (clear_bit_on_2nd_bitmap_for_kernel(pfn))
> >                    pfn_cache_private++;
> > +            /*
> > +             * NOTE: If THP for cache is introduced, the check for
> > +             *       compound pages is needed here.
> > +             */
> >            }
> >            /*
> >             * Exclude the data page of the user process.
> >             */
> > -        else if ((info->dump_level & DL_EXCLUDE_USER_DATA)
> > -            && isAnon(mapping)) {
> > -            if (clear_bit_on_2nd_bitmap_for_kernel(pfn))
> > -                pfn_user++;
> > +        else if (info->dump_level & DL_EXCLUDE_USER_DATA) {
> > +            /*
> > +             * Exclude the anonnymous pages as user pages.
> > +             */
> > +            if (isAnon(mapping)) {
> > +                if (clear_bit_on_2nd_bitmap_for_kernel(pfn))
> > +                    pfn_user++;
> > +
> > +                /*
> > +                 * Check the compound page
> > +                 */
> > +                if (page_is_hugepage(flags) && compound_order > 0) {
> > +                    int i, nr_pages = 1 << compound_order;
> > +
> > +                    for (i = 1; i < nr_pages; ++i) {
> > +                        if (clear_bit_on_2nd_bitmap_for_kernel(pfn + i))
> > +                            pfn_user++;
> > +                    }
> > +                    pfn += nr_pages - 2;
> > +                    mem_map += (nr_pages - 1) * SIZE(page);
> > +                }
> > +            }
> > +            /*
> > +             * Exclude the hugetlbfs pages as user pages.
> > +             */
> > +            else if (hugetlb_dtor == SYMBOL(free_huge_page)) {
> > +                int i, nr_pages = 1 << compound_order;
> > +
> > +                for (i = 0; i < nr_pages; ++i) {
> > +                    if (clear_bit_on_2nd_bitmap_for_kernel(pfn + i))
> > +                        pfn_user++;
> > +                }
> > +                pfn += nr_pages - 1;
> > +                mem_map += (nr_pages - 1) * SIZE(page);
> > +            }
> >            }
> >            /*
> >             * Exclude the hwpoison page.
>
> I'm concerned about the case that filtering is not performed to part of mem_map
> entries not belonging to the current cyclic range.
>
> If maximum value of compound_order is larger than maximum value of
> CONFIG_FORCE_MAX_ZONEORDER, which makedumpfile obtains by ARRAY_LENGTH(zone.free_area),
> it's necessary to align info->bufsize_cyclic with larger one in
> check_cyclic_buffer_overrun().

ping, in case you overlooked this...

--
Thanks.
HATAYAMA, Daisuke

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