mm: clarify why we avoid page_mapcount() for slab pages in dump_page()
Let's add comment on why we skip page_mapcount() for sl[aou]b pages. Link: http://lkml.kernel.org/r/20160922105532.GB24593@node Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -42,6 +42,11 @@ const struct trace_print_flags vmaflag_names[] = {
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void __dump_page(struct page *page, const char *reason)
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{
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/*
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* Avoid VM_BUG_ON() in page_mapcount().
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* page->_mapcount space in struct page is used by sl[aou]b pages to
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* encode own info.
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*/
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int mapcount = PageSlab(page) ? 0 : page_mapcount(page);
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pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx",
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