mm: remove PG_error

The PG_error bit is now unused; delete it and free up a bit in
page->flags.

Link: https://lkml.kernel.org/r/20240807193528.1865100-2-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/proc/page.c

@@ -182,7 +182,6 @@ u64 stable_page_flags(const struct page *page)
 #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_WRITEBACK,	PG_writeback);

include/linux/page-flags.h

@@ -66,8 +66,6 @@
  * PG_referenced, PG_reclaim are used for page reclaim for anonymous and
  * file-backed pagecache (see mm/vmscan.c).
  *
- * PG_error is set to indicate that an I/O error occurred on this page.
- *
  * PG_arch_1 is an architecture specific page state bit.  The generic code
  * guarantees that this bit is cleared for a page when it first is entered into
  * the page cache.
@@ -103,7 +101,6 @@ enum pageflags {
 	PG_waiters,		/* Page has waiters, check its waitqueue. Must be bit #7 and in the same byte as "PG_locked" */
 	PG_active,
 	PG_workingset,
-	PG_error,
 	PG_owner_priv_1,	/* Owner use. If pagecache, fs may use*/
 	PG_arch_1,
 	PG_reserved,
@@ -183,7 +180,7 @@ enum pageflags {
 	 */
 
 	/* At least one page in this folio has the hwpoison flag set */
-	PG_has_hwpoisoned = PG_error,
+	PG_has_hwpoisoned = PG_active,
 	PG_large_rmappable = PG_workingset, /* anon or file-backed */
 };
 
@@ -506,7 +503,6 @@ static inline int TestClearPage##uname(struct page *page) { return 0; }
 
 __PAGEFLAG(Locked, locked, PF_NO_TAIL)
 FOLIO_FLAG(waiters, FOLIO_HEAD_PAGE)
-PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL)
 FOLIO_FLAG(referenced, FOLIO_HEAD_PAGE)
 	FOLIO_TEST_CLEAR_FLAG(referenced, FOLIO_HEAD_PAGE)
 	__FOLIO_SET_FLAG(referenced, FOLIO_HEAD_PAGE)

include/trace/events/mmflags.h

@@ -100,7 +100,6 @@
 #define __def_pageflag_names						\
 	DEF_PAGEFLAG_NAME(locked),					\
 	DEF_PAGEFLAG_NAME(waiters),					\
-	DEF_PAGEFLAG_NAME(error),					\
 	DEF_PAGEFLAG_NAME(referenced),					\
 	DEF_PAGEFLAG_NAME(uptodate),					\
 	DEF_PAGEFLAG_NAME(dirty),					\

include/uapi/linux/kernel-page-flags.h

@@ -7,7 +7,7 @@
  */
 
 #define KPF_LOCKED		0
-#define KPF_ERROR		1
+#define KPF_ERROR		1	/* Now unused */
 #define KPF_REFERENCED		2
 #define KPF_UPTODATE		3
 #define KPF_DIRTY		4