[PATCH 10/10] proc: Rewrite stable_page_flags()

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

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.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Svetly Todorov <svetly.todorov@memverge.com>
---
 fs/proc/page.c             | 66 ++++++++++++++++++++------------------
 include/linux/huge_mm.h    |  4 +--
 include/linux/page-flags.h |  2 +-
 3 files changed, 38 insertions(+), 34 deletions(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 9223856c934b..d6953f95e3b4 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -107,10 +107,13 @@ static inline u64 kpf_copy_bit(u64 kflags, int ubit, int kbit)
 	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
@@ -118,49 +121,47 @@ u64 stable_page_flags(struct page *page)
 	 */
 	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 & 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
 	 * on the head page.
@@ -175,15 +176,15 @@ u64 stable_page_flags(struct page *page)
 	if (PageTable(page))
 		u |= 1 << KPF_PGTABLE;
 
-	if (page_is_idle(page))
+#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_SLAB,		PG_slab);
-	if (PageTail(page) && PageSlab(page))
-		u |= 1 << KPF_SLAB;
-
 	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);
@@ -194,7 +195,8 @@ u64 stable_page_flags(struct page *page)
 	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);
 
@@ -202,7 +204,10 @@ u64 stable_page_flags(struct page *page)
 	u |= kpf_copy_bit(k, KPF_MLOCKED,	PG_mlocked);
 
 #ifdef CONFIG_MEMORY_FAILURE
-	u |= kpf_copy_bit(k, KPF_HWPOISON,	PG_hwpoison);
+	if (u & 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
@@ -228,7 +233,6 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf,
 {
 	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;
@@ -245,9 +249,9 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf,
 		 * 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;
 		}
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 7576025db55d..1540a1481daf 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -351,7 +351,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf);
 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;
 }
@@ -480,7 +480,7 @@ static inline vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 	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;
 }
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index eaecf544039f..888353c209c0 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -734,7 +734,7 @@ static __always_inline bool PageKsm(const struct page *page)
 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.
-- 
2.43.0