On 01/20/2020 08:34 AM, Wei Yang wrote:
> This is a preparation to dump all reasons during check page.
This really makes sense rather then just picking the reason from
the last "if" statement.
>
> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
> ---
> include/linux/mmdebug.h | 2 +-
> mm/debug.c | 11 ++++++-----
> mm/page_alloc.c | 2 +-
> 3 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index 2ad72d2c8cc5..f0a612db8bae 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -10,7 +10,7 @@ struct vm_area_struct;
> struct mm_struct;
>
> extern void dump_page(struct page *page, const char *reason);
> -extern void __dump_page(struct page *page, const char *reason);
> +extern void __dump_page(struct page *page, int num, const char **reason);
> void dump_vma(const struct vm_area_struct *vma);
> void dump_mm(const struct mm_struct *mm);
>
> diff --git a/mm/debug.c b/mm/debug.c
> index 0461df1207cb..a8ac6f951f9f 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -42,11 +42,11 @@ const struct trace_print_flags vmaflag_names[] = {
> {0, NULL}
> };
>
> -void __dump_page(struct page *page, const char *reason)
> +void __dump_page(struct page *page, int num, const char **reason)
> {
> struct address_space *mapping;
> bool page_poisoned = PagePoisoned(page);
> - int mapcount;
> + int mapcount, i;
>
> /*
> * If struct page is poisoned don't access Page*() functions as that
> @@ -97,8 +97,9 @@ void __dump_page(struct page *page, const char *reason)
> sizeof(unsigned long), page,
> sizeof(struct page), false);
>
> - if (reason)
> - pr_warn("page dumped because: %s\n", reason);
> + pr_warn("page dumped because:\n");
> + for (i = 0; i < num; i++)
> + pr_warn("\t%s\n", reason[i]);
We should have a NR_BAD_PAGE_REASONS or something to cap this iteration
and also check reason[i] for non-NULL before trying to print the array.
There might be call sites like the following which will be problematic
otherwise.
split_huge_page_to_list() -> dump_page(head, NULL)
>
> #ifdef CONFIG_MEMCG
> if (!page_poisoned && page->mem_cgroup)
While here, will it be better to move the above debug print block after
mem_cgroup block instead ?
> @@ -108,7 +109,7 @@ void __dump_page(struct page *page, const char *reason)
>
> void dump_page(struct page *page, const char *reason)
> {
> - __dump_page(page, reason);
> + __dump_page(page, 1, &reason);
> dump_page_owner(page);
> }
> EXPORT_SYMBOL(dump_page);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d047bf7d8fd4..0cf6218aaba7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -638,7 +638,7 @@ static void bad_page(struct page *page, const char *reason,
>
> pr_alert("BUG: Bad page state in process %s pfn:%05lx\n",
> current->comm, page_to_pfn(page));
> - __dump_page(page, reason);
> + __dump_page(page, 1, &reason);
> bad_flags &= page->flags;
> if (bad_flags)
> pr_alert("bad because of flags: %#lx(%pGp)\n",
>
Do we still need to have bad_flags ? After consolidating all reasons making
a page bad should not we just print page->flags unconditionally each time and
let the user decipher it instead. __dump_page() will print page->flags for
each case (atleast after the new patch from Vlastimil). AFAICS, the only
place currently consuming bad_flags is bad_page() which seems redundant after
first calling __dump_page().
