On 3/21/24 15:24, Matthew Wilcox (Oracle) wrote:
> For pages that have a page_type, set the mapcount to 0, which will
> reduce the confusion in people reading page dumps ("Why does this page
> have a mapcount of -128?"). Now that hugetlbfs is a page_type, read the
> entire_mapcount for any large folio; this is fine for all folios as no
> user reuses the entire_mapcount field.
>
> For pages which do not have a page type, do not print it to reduce
> clutter.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/debug.c | 19 ++++++++-----------
> 1 file changed, 8 insertions(+), 11 deletions(-)
>
> diff --git a/mm/debug.c b/mm/debug.c
> index c1c1a6a484e4..e8a96b8b7197 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -55,18 +55,14 @@ static void __dump_folio(struct folio *folio, struct page *page,
> unsigned long pfn, unsigned long idx)
> {
> struct address_space *mapping = folio_mapping(folio);
> - int mapcount = 0;
> + int mapcount = atomic_read(&page->_mapcount) + 1;
> char *type = "";
>
> - /*
> - * page->_mapcount space in struct page is used by slab pages to
> - * encode own info, and we must avoid calling page_folio() again.
> - */
> - if (!folio_test_slab(folio)) {
> - mapcount = atomic_read(&page->_mapcount) + 1;
> - if (folio_test_large(folio))
> - mapcount += folio_entire_mapcount(folio);
> - }
> + /* Open-code page_mapcount() to avoid looking up a stale folio */
> + if (mapcount < 0)
> + mapcount = 0;
> + if (folio_test_large(folio))
> + mapcount += folio_entire_mapcount(folio);
>
> pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n",
> folio_ref_count(folio), mapcount, mapping,
> @@ -99,7 +95,8 @@ static void __dump_folio(struct folio *folio, struct page *page,
> */
> pr_warn("%sflags: %pGp%s\n", type, &folio->flags,
> is_migrate_cma_folio(folio, pfn) ? " CMA" : "");
> - pr_warn("page_type: %pGt\n", &folio->page.page_type);
> + if (page_has_type(&folio->page))
> + pr_warn("page_type: %pGt\n", &folio->page.page_type);
>
> print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
> sizeof(unsigned long), page,
