Re: [PATCH 1/5] mm: print more information about mapping in __dump_page

Anshuman Khandual
2018-11-16T11:56:02Z

On 11/16/2018 02:00 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> __dump_page prints the mapping pointer but that is quite unhelpful
> for many reports because the pointer itself only helps to distinguish
> anon/ksm mappings from other ones (because of lowest bits
> set). Sometimes it would be much more helpful to know what kind of
> mapping that is actually and if we know this is a file mapping then also
> try to resolve the dentry name.
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/debug.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/mm/debug.c b/mm/debug.c
> index cdacba12e09a..a33177bfc856 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -44,6 +44,7 @@ const struct trace_print_flags vmaflag_names[] = {
>
> void __dump_page(struct page *page, const char *reason)
> {
> + struct address_space *mapping = page_mapping(page);
> bool page_poisoned = PagePoisoned(page);
> int mapcount;
>
> @@ -70,6 +71,18 @@ void __dump_page(struct page *page, const char *reason)
> if (PageCompound(page))
> pr_cont(" compound_mapcount: %d", compound_mapcount(page));
> pr_cont("\n");
> + if (PageAnon(page))
> + pr_emerg("anon ");
> + else if (PageKsm(page))
> + pr_emerg("ksm ");
> + else if (mapping) {
> + pr_emerg("%ps ", mapping->a_ops);
> + if (mapping->host->i_dentry.first) {
> + struct dentry *dentry;
> + dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias);
> + pr_emerg("name:\"%*s\" ", dentry->d_name.len, dentry->d_name.name);
> + }
> + }
> BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
>
> pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>

Differentiating between anon, ksm mapping and going till dentry information
for file mappings is surely an improvement.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>