Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages()

[Vlastimil Babka]

On 1/14/20 10:10 AM, Michal Hocko wrote:
> [Cc Ralph]
>> The reason is dump_page() does not print page->flags universally
>> and only does so for KSM, Anon and File pages while excluding
>> reserved pages at boot. Wondering should not we make printing
>> page->flags universal ?
> 
> We used to do that and this caught me as a surprise when looking again.
> This is a result of 76a1850e4572 ("mm/debug.c: __dump_page() prints an
> extra line") which is a cleanup patch and I suspect this result was not
> anticipated.
> 
> The following will do the trick but I cannot really say I like the code
> duplication. pr_cont in this case sounds like a much cleaner solution to
> me.

How about this then?

diff --git mm/debug.c mm/debug.c
index 0461df1207cb..6a52316af839 100644
--- mm/debug.c
+++ mm/debug.c
@@ -47,6 +47,7 @@ void __dump_page(struct page *page, const char *reason)
 	struct address_space *mapping;
 	bool page_poisoned = PagePoisoned(page);
 	int mapcount;
+	char *type = "";
 
 	/*
 	 * If struct page is poisoned don't access Page*() functions as that
@@ -78,9 +79,9 @@ void __dump_page(struct page *page, const char *reason)
 			page, page_ref_count(page), mapcount,
 			page->mapping, page_to_pgoff(page));
 	if (PageKsm(page))
-		pr_warn("ksm flags: %#lx(%pGp)\n", page->flags, &page->flags);
+		type = "ksm ";
 	else if (PageAnon(page))
-		pr_warn("anon flags: %#lx(%pGp)\n", page->flags, &page->flags);
+		type = "anon ";
 	else if (mapping) {
 		if (mapping->host && mapping->host->i_dentry.first) {
 			struct dentry *dentry;
@@ -88,10 +89,11 @@ void __dump_page(struct page *page, const char *reason)
 			pr_warn("%ps name:\"%pd\"\n", mapping->a_ops, dentry);
 		} else
 			pr_warn("%ps\n", mapping->a_ops);
-		pr_warn("flags: %#lx(%pGp)\n", page->flags, &page->flags);
 	}
 	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
 
+	pr_warn("%sflags: %#lx(%pGp)\n", type, page->flags, &page->flags);
+
 hex_only:
 	print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
 			sizeof(unsigned long), page,