The patch titled
Subject: mm: improve dumping of mapcount and page_type
has been added to the -mm mm-unstable branch. Its filename is
mm-improve-dumping-of-mapcount-and-page_type.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-improve-dumping-of-mapcount-and-page_type.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm: improve dumping of mapcount and page_type
Date: Thu, 21 Mar 2024 14:24:46 +0000
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.
Link: https://lkml.kernel.org/r/20240321142448.1645400-9-willy@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/debug.c | 19 ++++++++-----------
1 file changed, 8 insertions(+), 11 deletions(-)
--- a/mm/debug.c~mm-improve-dumping-of-mapcount-and-page_type
+++ a/mm/debug.c
@@ -55,18 +55,14 @@ static void __dump_folio(struct folio *f
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 *f
*/
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,
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
mm-increase-folio-batch-size.patch
mm-always-initialise-folio-_deferred_list.patch
mm-create-folio_flag_false-and-folio_type_ops-macros.patch
mm-remove-folio_prep_large_rmappable.patch
mm-support-page_mapcount-on-page_has_type-pages.patch
mm-turn-folio_test_hugetlb-into-a-pagetype.patch
mm-remove-a-call-to-compound_head-from-is_page_hwpoison.patch
mm-free-up-pg_slab.patch
mm-improve-dumping-of-mapcount-and-page_type.patch
hugetlb-remove-mention-of-destructors.patch
