When debugging a problem that involves compound pages, it is extremely helpful if dump_page() reports not only the page->_refcount, but also the refcount of the head page of the compound page. That's because the head page collects refcounts for the entire compound page.
Therefore, enhance dump_page() so as to print out the refcount of the head page of a compound page.
This approach (printing information about a struct page that is not the struct page that was passed into dump_page()) has a precedent: compound_mapcount is already being printed.
Signed-off-by: John Hubbard jhubbard@nvidia.com --- mm/debug.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/debug.c b/mm/debug.c index a90da5337c14..4cc6cad8385d 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -76,9 +76,11 @@ void __dump_page(struct page *page, const char *reason) mapcount = PageSlab(page) ? 0 : page_mapcount(page);
if (PageCompound(page)) - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " - "index:%#lx compound_mapcount: %d\n", - page, page_ref_count(page), mapcount, + pr_warn("page:%px refcount:%d head refcount:%d " + "mapcount:%d mapping:%px index:%#lx " + "compound_mapcount:%d\n", + page, page_ref_count(page), + page_ref_count(compound_head(page)), mapcount, page->mapping, page_to_pgoff(page), compound_mapcount(page)); else