proc: rewrite stable_page_flags()

Reduce the usage of PageFlag tests and reduce the number of
compound_head() calls.

For multi-page folios, we'll now show all pages as having the flags that
apply to them, e.g. if it's dirty, all pages will have the dirty flag set
instead of just the head page. The mapped flag is still per page, as is
the hwpoison flag.

[[e-mail]: fix up some bits vs masks]
Link: https://lkml.kernel.org/r/[e-mail]
[[e-mail]: fix warnings]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Reviewed-by: Svetly Todorov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

fs/proc/page.c

···
 	return ((kflags >> kbit) & 1) << ubit;
 }
 
-u64 stable_page_flags(struct page *page)
+u64 stable_page_flags(const struct page *page)
 {
-	u64 k;
-	u64 u;
+	const struct folio *folio;
+	unsigned long k;
+	unsigned long mapping;
+	bool is_anon;
+	u64 u = 0;
 
 	/*
 	 * pseudo flag: KPF_NOPAGE
···
 	 */
 	if (!page)
 		return 1 << KPF_NOPAGE;
+	folio = page_folio(page);
 
-	k = page->flags;
-	u = 0;
+	k = folio->flags;
+	mapping = (unsigned long)folio->mapping;
+	is_anon = mapping & PAGE_MAPPING_ANON;
 
 	/*
 	 * pseudo flags for the well known (anonymous) memory mapped pages
 	 */
 	if (page_mapped(page))
 		u |= 1 << KPF_MMAP;
-	if (PageAnon(page))
+	if (is_anon) {
 		u |= 1 << KPF_ANON;
-	if (PageKsm(page))
-		u |= 1 << KPF_KSM;
+		if (mapping & PAGE_MAPPING_KSM)
+			u |= 1 << KPF_KSM;
+	}
 
 	/*
 	 * compound pages: export both head/tail info
 	 * they together define a compound page's start/end pos and order
 	 */
-	if (PageHead(page))
-		u |= 1 << KPF_COMPOUND_HEAD;
-	if (PageTail(page))
+	if (page == &folio->page)
+		u |= kpf_copy_bit(k, KPF_COMPOUND_HEAD, PG_head);
+	else
 		u |= 1 << KPF_COMPOUND_TAIL;
-	if (PageHuge(page))
+	if (folio_test_hugetlb(folio))
 		u |= 1 << KPF_HUGE;
 	/*
-	 * PageTransCompound can be true for non-huge compound pages (slab
-	 * pages or pages allocated by drivers with __GFP_COMP) because it
-	 * just checks PG_head/PG_tail, so we need to check PageLRU/PageAnon
+	 * We need to check PageLRU/PageAnon
 	 * to make sure a given page is a thp, not a non-huge compound page.
 	 */
-	else if (PageTransCompound(page)) {
-		struct page *head = compound_head(page);
-
-		if (PageLRU(head) || PageAnon(head))
+	else if (folio_test_large(folio)) {
+		if ((k & (1 << PG_lru)) || is_anon)
 			u |= 1 << KPF_THP;
-		else if (is_huge_zero_page(head)) {
+		else if (is_huge_zero_page(&folio->page)) {
 			u |= 1 << KPF_ZERO_PAGE;
 			u |= 1 << KPF_THP;
 		}
 	} else if (is_zero_pfn(page_to_pfn(page)))
 		u |= 1 << KPF_ZERO_PAGE;
-
 
 	/*
 	 * Caveats on high order pages: PG_buddy and PG_slab will only be set
···
 		u |= 1 << KPF_OFFLINE;
 	if (PageTable(page))
 		u |= 1 << KPF_PGTABLE;
-
-	if (page_is_idle(page))
-		u |= 1 << KPF_IDLE;
-
-	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
-
-	u |= kpf_copy_bit(k, KPF_SLAB,		PG_slab);
-	if (PageTail(page) && PageSlab(page))
+	if (folio_test_slab(folio))
 		u |= 1 << KPF_SLAB;
 
+#if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
+	u |= kpf_copy_bit(k, KPF_IDLE,          PG_idle);
+#else
+	if (folio_test_idle(folio))
+		u |= 1 << KPF_IDLE;
+#endif
+
+	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
 	u |= kpf_copy_bit(k, KPF_ERROR,		PG_error);
 	u |= kpf_copy_bit(k, KPF_DIRTY,		PG_dirty);
 	u |= kpf_copy_bit(k, KPF_UPTODATE,	PG_uptodate);
···
 	u |= kpf_copy_bit(k, KPF_ACTIVE,	PG_active);
 	u |= kpf_copy_bit(k, KPF_RECLAIM,	PG_reclaim);
 
-	if (PageSwapCache(page))
+#define SWAPCACHE ((1 << PG_swapbacked) | (1 << PG_swapcache))
+	if ((k & SWAPCACHE) == SWAPCACHE)
 		u |= 1 << KPF_SWAPCACHE;
 	u |= kpf_copy_bit(k, KPF_SWAPBACKED,	PG_swapbacked);
 
···
 	u |= kpf_copy_bit(k, KPF_MLOCKED,	PG_mlocked);
 
 #ifdef CONFIG_MEMORY_FAILURE
-	u |= kpf_copy_bit(k, KPF_HWPOISON,	PG_hwpoison);
+	if (u & (1 << KPF_HUGE))
+		u |= kpf_copy_bit(k, KPF_HWPOISON,	PG_hwpoison);
+	else
+		u |= kpf_copy_bit(page->flags, KPF_HWPOISON,	PG_hwpoison);
 #endif
 
 #ifdef CONFIG_ARCH_USES_PG_UNCACHED
···
 {
 	const unsigned long max_dump_pfn = get_max_dump_pfn();
 	u64 __user *out = (u64 __user *)buf;
-	struct page *ppage;
 	unsigned long src = *ppos;
 	unsigned long pfn;
 	ssize_t ret = 0;
···
 		 * TODO: ZONE_DEVICE support requires to identify
 		 * memmaps that were actually initialized.
 		 */
-		ppage = pfn_to_online_page(pfn);
+		struct page *page = pfn_to_online_page(pfn);
 
-		if (put_user(stable_page_flags(ppage), out)) {
+		if (put_user(stable_page_flags(page), out)) {
 			ret = -EFAULT;
 			break;
 		}

include/linux/huge_mm.h

···
 extern struct page *huge_zero_page;
 extern unsigned long huge_zero_pfn;
 
-static inline bool is_huge_zero_page(struct page *page)
+static inline bool is_huge_zero_page(const struct page *page)
 {
 	return READ_ONCE(huge_zero_page) == page;
 }
···
 	return 0;
 }
 
-static inline bool is_huge_zero_page(struct page *page)
+static inline bool is_huge_zero_page(const struct page *page)
 {
 	return false;
 }

include/linux/page-flags.h

···
 TESTPAGEFLAG_FALSE(Ksm, ksm)
 #endif
 
-u64 stable_page_flags(struct page *page);
+u64 stable_page_flags(const struct page *page);
 
 /**
  * folio_xor_flags_has_waiters - Change some folio flags.

tools/cgroup/memcg_slabinfo.py

···
 
 
 def for_each_slab(prog):
-    PGSlab = 1 << prog.constant('PG_slab')
-    PGHead = 1 << prog.constant('PG_head')
+    PGSlab = ~prog.constant('PG_slab')
 
     for page in for_each_page(prog):
         try:
-            if page.flags.value_() & PGSlab:
+            if page.page_type.value_() == PGSlab:
                 yield cast('struct slab *', page)
         except FaultError:
             pass