Re: [PATCH 1/2] mm: Turn folio_test_hugetlb into a PageType

[Matthew Wilcox <willy@infradead.org>]

On Thu, Mar 14, 2024 at 11:26:17AM +0100, David Hildenbrand wrote:
> Should we include this hunk:
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index c1c1a6a484e4c..f521e17150a10 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -63,7 +63,8 @@ static void __dump_folio(struct folio *folio, struct page *page,
>          * 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_hugetlb(folio))
> +                       mapcount = atomic_read(&page->_mapcount) + 1;
>                 if (folio_test_large(folio))
>                         mapcount += folio_entire_mapcount(folio);
>         }
> 
> Apart from that, LGTM

I actually want to do a bit more here ...

+++ b/mm/debug.c
@@ -58,15 +58,10 @@ static void __dump_folio(struct folio *folio, struct page *page,
        int mapcount = 0;
        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)) {
+       if (!page_has_type(page)) {
                mapcount = atomic_read(&page->_mapcount) + 1;
-               if (folio_test_large(folio))
-                       mapcount += folio_entire_mapcount(folio);
-       }
+       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 +94,8 @@ 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(page))
+               pr_warn("type: %pGt\n", &folio->page.page_type);

        print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
                        sizeof(unsigned long), page,


and I think that deserves its own patch.

Also, I need to do:

+++ b/include/trace/events/mmflags.h
@@ -135,6 +135,7 @@ IF_HAVE_PG_ARCH_X(arch_3)
 #define DEF_PAGETYPE_NAME(_name) { PG_##_name, __stringify(_name) }

 #define __def_pagetype_names                                           \
+       DEF_PAGETYPE_NAME(hugetlb)                                      \
        DEF_PAGETYPE_NAME(offline),                                     \
        DEF_PAGETYPE_NAME(guard),                                       \
        DEF_PAGETYPE_NAME(table),                                       \

(and I think having this in the include/trace directory is a mistake;
putting it in page-flags.h will lead to it not being forgotten)