[PATCH v2] makedumpfile: Exclude unnecessary hugepages.

[bhe at redhat.com]

On 07/17/14 at 06:34am, Atsushi Kumagai wrote:
> Hello Baoquan,
> 
> >On 06/17/14 at 02:32am, Atsushi Kumagai wrote:
> >> +		else if (info->dump_level & DL_EXCLUDE_USER_DATA) {
> >Hi Atsushi,
> >
> >Could it be changed to checking hugepage first, then anonymous page?
> >This can avoid involving the free_huge_page.
> >
> >like this:
> >	int nr_pages;
> >	if (page_is_hugepage(flags) {
> >		int nr_pages = 1 << compound_order;
> >
> >		exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
> >
> >		pfn += nr_pages - 1;
> >		mem_map += (nr_pages - 1) * SIZE(page);
> >	} else if (isAnon(mapping)) {
> >		int nr_pages = 1;
> >
> >		exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
> >
> >		pfn += nr_pages - 1;
> >		mem_map += (nr_pages - 1) * SIZE(page);
> >	}
> >
> >But I may not know the meaning of free_huge_page completely. If you
> >think introducing free_huge_page is better, I am fine too, can ACK that
> >kernel patch to export free_huge_page you posted.
> 
> The assumption that all compound pages are user pages is wrong since some
> kernel pages can be compound. For example, kmalloc_large_node() calls 
> alloc_pages_node() with __GFP_COMP. This means we have to check compound
> user pages without only depending on page_is_hugepage(). We can detect THPs
> with the combination of page_is_hugepage() and isAnon(), but it can't be
> applied to hugetlbfs pages.
> This is why we need to export free_huge_page.
> 
> BTW, the v2 code can misdetect hugetlbfs due to the wrong check order, 
> I'm going to fix it in the next version.

Yeah, I checked that and found it's related to slub implementation.

But if hugetlbfs is used by kernel space, current checking condition
may not be enough. Anyway, expect your new post of v3.

> 
> 
> Thanks
> Atsushi Kumagai
> 
> >Thanks
> >Baoquan
> >
> >> +			/*
> >> +			 * Exclude the anonymous pages as user pages.
> >> +			 */
> >> +			if (isAnon(mapping)) {
> >> +				int nr_pages;
> >> +				/*
> >> +				 * Check the compound page
> >> +				 */
> >> +				if (page_is_hugepage(flags) && compound_order > 0)
> >> +					nr_pages = 1 << compound_order;
> >> +				else
> >> +					nr_pages = 1;
> >> +
> >> +				exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
> >> +
> >> +				pfn += nr_pages - 1;
> >> +				mem_map += (nr_pages - 1) * SIZE(page);
> >> +			}
> >> +			/*
> >> +			 * Exclude the hugetlbfs pages as user pages.
> >> +			 */
> >> +			else if (hugetlb_dtor == SYMBOL(free_huge_page)) {
> >> +				int nr_pages = 1 << compound_order;
> >> +
> >> +				exclude_range(&pfn_user, pfn, pfn + nr_pages, cycle);
> >> +
> >> +				pfn += nr_pages - 1;
> >> +				mem_map += (nr_pages - 1) * SIZE(page);
> >> +			}
> >>  		}
> >
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> 
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