[PATCH 8/8] mm: Remove PG_reclaim

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Nobody sets the flag anymore.

Remove the PG_reclaim, making PG_readhead exclusive user of the page
flag bit.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 fs/fuse/dev.c                          |  2 +-
 fs/proc/page.c                         |  2 +-
 include/linux/mm_inline.h              |  1 -
 include/linux/page-flags.h             | 15 +++++----------
 include/trace/events/mmflags.h         |  2 +-
 include/uapi/linux/kernel-page-flags.h |  2 +-
 mm/filemap.c                           | 12 ------------
 mm/migrate.c                           | 10 ++--------
 mm/page-writeback.c                    | 16 +---------------
 mm/page_io.c                           | 15 +++++----------
 mm/swap.c                              | 16 ----------------
 mm/vmscan.c                            |  7 -------
 tools/mm/page-types.c                  |  8 +-------
 13 files changed, 18 insertions(+), 90 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 27ccae63495d..20005e2e1d28 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -827,7 +827,7 @@ static int fuse_check_folio(struct folio *folio)
 	       1 << PG_lru |
 	       1 << PG_active |
 	       1 << PG_workingset |
-	       1 << PG_reclaim |
+	       1 << PG_readahead |
 	       1 << PG_waiters |
 	       LRU_GEN_MASK | LRU_REFS_MASK))) {
 		dump_page(&folio->page, "fuse: trying to steal weird page");
diff --git a/fs/proc/page.c b/fs/proc/page.c
index a55f5acefa97..59860ba2393c 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -189,7 +189,7 @@ u64 stable_page_flags(const struct page *page)
 	u |= kpf_copy_bit(k, KPF_LRU,		PG_lru);
 	u |= kpf_copy_bit(k, KPF_REFERENCED,	PG_referenced);
 	u |= kpf_copy_bit(k, KPF_ACTIVE,	PG_active);
-	u |= kpf_copy_bit(k, KPF_RECLAIM,	PG_reclaim);
+	u |= kpf_copy_bit(k, KPF_READAHEAD,	PG_readahead);
 
 #define SWAPCACHE ((1 << PG_swapbacked) | (1 << PG_swapcache))
 	if ((k & SWAPCACHE) == SWAPCACHE)
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index f353d3c610ac..269acf1f77b4 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -270,7 +270,6 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
 	set_mask_bits(&folio->flags, LRU_GEN_MASK | BIT(PG_active), flags);
 
 	lru_gen_update_size(lruvec, folio, -1, gen);
-	/* for folio_rotate_reclaimable() */
 	if (reclaiming)
 		list_add_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
 	else
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 2414e7921eea..8f59fd8b86c9 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -63,8 +63,8 @@
  * might lose their PG_swapbacked flag when they simply can be dropped (e.g. as
  * a result of MADV_FREE).
  *
- * PG_referenced, PG_reclaim are used for page reclaim for anonymous and
- * file-backed pagecache (see mm/vmscan.c).
+ * PG_referenced is used for page reclaim for anonymous and file-backed
+ * pagecache (see mm/vmscan.c).
  *
  * 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
@@ -107,7 +107,7 @@ enum pageflags {
 	PG_reserved,
 	PG_private,		/* If pagecache, has fs-private data */
 	PG_private_2,		/* If pagecache, has fs aux data */
-	PG_reclaim,		/* To be reclaimed asap */
+	PG_readahead,
 	PG_swapbacked,		/* Page is backed by RAM/swap */
 	PG_unevictable,		/* Page is "unevictable"  */
 	PG_dropbehind,		/* drop pages on IO completion */
@@ -129,8 +129,6 @@ enum pageflags {
 #endif
 	__NR_PAGEFLAGS,
 
-	PG_readahead = PG_reclaim,
-
 	/* Anonymous memory (and shmem) */
 	PG_swapcache = PG_owner_priv_1, /* Swap page: swp_entry_t in private */
 	/* Some filesystems */
@@ -168,7 +166,7 @@ enum pageflags {
 	PG_xen_remapped = PG_owner_priv_1,
 
 	/* non-lru isolated movable page */
-	PG_isolated = PG_reclaim,
+	PG_isolated = PG_readahead,
 
 	/* Only valid for buddy pages. Used to track pages that are reported */
 	PG_reported = PG_uptodate,
@@ -187,7 +185,7 @@ enum pageflags {
 	/* At least one page in this folio has the hwpoison flag set */
 	PG_has_hwpoisoned = PG_active,
 	PG_large_rmappable = PG_workingset, /* anon or file-backed */
-	PG_partially_mapped = PG_reclaim, /* was identified to be partially mapped */
+	PG_partially_mapped = PG_readahead, /* was identified to be partially mapped */
 };
 
 #define PAGEFLAGS_MASK		((1UL << NR_PAGEFLAGS) - 1)
@@ -594,9 +592,6 @@ TESTPAGEFLAG(Writeback, writeback, PF_NO_TAIL)
 	TESTSCFLAG(Writeback, writeback, PF_NO_TAIL)
 FOLIO_FLAG(mappedtodisk, FOLIO_HEAD_PAGE)
 
-/* PG_readahead is only used for reads; PG_reclaim is only for writes */
-PAGEFLAG(Reclaim, reclaim, PF_NO_TAIL)
-	TESTCLEARFLAG(Reclaim, reclaim, PF_NO_TAIL)
 FOLIO_FLAG(readahead, FOLIO_HEAD_PAGE)
 	FOLIO_TEST_CLEAR_FLAG(readahead, FOLIO_HEAD_PAGE)
 
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 3bc8656c8359..15d92784a745 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -114,7 +114,7 @@
 	DEF_PAGEFLAG_NAME(private_2),					\
 	DEF_PAGEFLAG_NAME(writeback),					\
 	DEF_PAGEFLAG_NAME(head),					\
-	DEF_PAGEFLAG_NAME(reclaim),					\
+	DEF_PAGEFLAG_NAME(readahead),					\
 	DEF_PAGEFLAG_NAME(swapbacked),					\
 	DEF_PAGEFLAG_NAME(unevictable),					\
 	DEF_PAGEFLAG_NAME(dropbehind)					\
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index ff8032227876..e5a9a113e079 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -15,7 +15,7 @@
 #define KPF_ACTIVE		6
 #define KPF_SLAB		7
 #define KPF_WRITEBACK		8
-#define KPF_RECLAIM		9
+#define KPF_READAHEAD		9
 #define KPF_BUDDY		10
 
 /* 11-20: new additions in 2.6.31 */
diff --git a/mm/filemap.c b/mm/filemap.c
index 5ca26f5e7238..8951c37c8a38 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1624,18 +1624,6 @@ void folio_end_writeback(struct folio *folio)
 
 	VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
 
-	/*
-	 * folio_test_clear_reclaim() could be used here but it is an
-	 * atomic operation and overkill in this particular case. Failing
-	 * to shuffle a folio marked for immediate reclaim is too mild
-	 * a gain to justify taking an atomic operation penalty at the
-	 * end of every folio writeback.
-	 */
-	if (folio_test_reclaim(folio)) {
-		folio_clear_reclaim(folio);
-		folio_rotate_reclaimable(folio);
-	}
-
 	/*
 	 * Writeback does not hold a folio reference of its own, relying
 	 * on truncation to wait for the clearing of PG_writeback.
diff --git a/mm/migrate.c b/mm/migrate.c
index caadbe393aa2..beba72da5e33 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -686,6 +686,8 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
 		folio_set_young(newfolio);
 	if (folio_test_idle(folio))
 		folio_set_idle(newfolio);
+	if (folio_test_readahead(folio))
+		folio_set_readahead(newfolio);
 
 	folio_migrate_refs(newfolio, folio);
 	/*
@@ -728,14 +730,6 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
 	if (folio_test_writeback(newfolio))
 		folio_end_writeback(newfolio);
 
-	/*
-	 * PG_readahead shares the same bit with PG_reclaim.  The above
-	 * end_page_writeback() may clear PG_readahead mistakenly, so set the
-	 * bit after that.
-	 */
-	if (folio_test_readahead(folio))
-		folio_set_readahead(newfolio);
-
 	folio_copy_owner(newfolio, folio);
 	pgalloc_tag_swap(newfolio, folio);
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4f5970723cf2..f2b94a2cbfcf 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2888,22 +2888,8 @@ bool folio_mark_dirty(struct folio *folio)
 {
 	struct address_space *mapping = folio_mapping(folio);
 
-	if (likely(mapping)) {
-		/*
-		 * readahead/folio_deactivate could remain
-		 * PG_readahead/PG_reclaim due to race with folio_end_writeback
-		 * About readahead, if the folio is written, the flags would be
-		 * reset. So no problem.
-		 * About folio_deactivate, if the folio is redirtied,
-		 * the flag will be reset. So no problem. but if the
-		 * folio is used by readahead it will confuse readahead
-		 * and make it restart the size rampup process. But it's
-		 * a trivial problem.
-		 */
-		if (folio_test_reclaim(folio))
-			folio_clear_reclaim(folio);
+	if (likely(mapping))
 		return mapping->a_ops->dirty_folio(mapping, folio);
-	}
 
 	return noop_dirty_folio(mapping, folio);
 }
diff --git a/mm/page_io.c b/mm/page_io.c
index 9b983de351f9..0cb71f318fb1 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -37,14 +37,11 @@ static void __end_swap_bio_write(struct bio *bio)
 		 * Re-dirty the page in order to avoid it being reclaimed.
 		 * Also print a dire warning that things will go BAD (tm)
 		 * very quickly.
-		 *
-		 * Also clear PG_reclaim to avoid folio_rotate_reclaimable()
 		 */
 		folio_mark_dirty(folio);
 		pr_alert_ratelimited("Write-error on swap-device (%u:%u:%llu)\n",
 				     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
 				     (unsigned long long)bio->bi_iter.bi_sector);
-		folio_clear_reclaim(folio);
 	}
 	folio_end_writeback(folio);
 }
@@ -350,19 +347,17 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
 
 	if (ret != sio->len) {
 		/*
-		 * In the case of swap-over-nfs, this can be a
-		 * temporary failure if the system has limited
-		 * memory for allocating transmit buffers.
-		 * Mark the page dirty and avoid
-		 * folio_rotate_reclaimable but rate-limit the
-		 * messages.
+		 * In the case of swap-over-nfs, this can be a temporary failure
+		 * if the system has limited memory for allocating transmit
+		 * buffers.
+		 *
+		 * Mark the page dirty but rate-limit the messages.
 		 */
 		pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
 				   ret, swap_dev_pos(page_swap_entry(page)));
 		for (p = 0; p < sio->pages; p++) {
 			page = sio->bvec[p].bv_page;
 			set_page_dirty(page);
-			ClearPageReclaim(page);
 		}
 	}
 
diff --git a/mm/swap.c b/mm/swap.c
index 4eb33b4804a8..5b94f13821e3 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -221,22 +221,6 @@ static void lru_move_tail(struct lruvec *lruvec, struct folio *folio)
 	__count_vm_events(PGROTATED, folio_nr_pages(folio));
 }
 
-/*
- * Writeback is about to end against a folio which has been marked for
- * immediate reclaim.  If it still appears to be reclaimable, move it
- * to the tail of the inactive list.
- *
- * folio_rotate_reclaimable() must disable IRQs, to prevent nasty races.
- */
-void folio_rotate_reclaimable(struct folio *folio)
-{
-	if (folio_test_locked(folio) || folio_test_dirty(folio) ||
-	    folio_test_unevictable(folio))
-		return;
-
-	folio_batch_add_and_move(folio, lru_move_tail, true);
-}
-
 void lru_note_cost(struct lruvec *lruvec, bool file,
 		   unsigned int nr_io, unsigned int nr_rotated)
 {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bb5ec22f97b5..e61e88e63511 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3216,9 +3216,6 @@ static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclai
 
 		new_flags = old_flags & ~(LRU_GEN_MASK | LRU_REFS_FLAGS);
 		new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
-		/* for folio_end_writeback() */
-		if (reclaiming)
-			new_flags |= BIT(PG_reclaim);
 	} while (!try_cmpxchg(&folio->flags, &old_flags, new_flags));
 
 	lru_gen_update_size(lruvec, folio, old_gen, new_gen);
@@ -4460,9 +4457,6 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
 	if (!folio_test_referenced(folio))
 		set_mask_bits(&folio->flags, LRU_REFS_MASK, 0);
 
-	/* for shrink_folio_list() */
-	folio_clear_reclaim(folio);
-
 	success = lru_gen_del_folio(lruvec, folio, true);
 	VM_WARN_ON_ONCE_FOLIO(!success, folio);
 
@@ -4659,7 +4653,6 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
 			continue;
 		}
 
-		/* retry folios that may have missed folio_rotate_reclaimable() */
 		if (!skip_retry && !folio_test_active(folio) && !folio_mapped(folio) &&
 		    !folio_test_dirty(folio) && !folio_test_writeback(folio)) {
 			list_move(&folio->lru, &clean);
diff --git a/tools/mm/page-types.c b/tools/mm/page-types.c
index bcac7ebfb51f..c06647501370 100644
--- a/tools/mm/page-types.c
+++ b/tools/mm/page-types.c
@@ -85,7 +85,6 @@
  * not part of kernel API
  */
 #define KPF_ANON_EXCLUSIVE	47
-#define KPF_READAHEAD		48
 #define KPF_SLUB_FROZEN		50
 #define KPF_SLUB_DEBUG		51
 #define KPF_FILE		61
@@ -108,7 +107,7 @@ static const char * const page_flag_names[] = {
 	[KPF_ACTIVE]		= "A:active",
 	[KPF_SLAB]		= "S:slab",
 	[KPF_WRITEBACK]		= "W:writeback",
-	[KPF_RECLAIM]		= "I:reclaim",
+	[KPF_READAHEAD]		= "I:readahead",
 	[KPF_BUDDY]		= "B:buddy",
 
 	[KPF_MMAP]		= "M:mmap",
@@ -139,7 +138,6 @@ static const char * const page_flag_names[] = {
 	[KPF_ARCH_2]		= "H:arch_2",
 
 	[KPF_ANON_EXCLUSIVE]	= "d:anon_exclusive",
-	[KPF_READAHEAD]		= "I:readahead",
 	[KPF_SLUB_FROZEN]	= "A:slub_frozen",
 	[KPF_SLUB_DEBUG]	= "E:slub_debug",
 
@@ -484,10 +482,6 @@ static uint64_t expand_overloaded_flags(uint64_t flags, uint64_t pme)
 			flags ^= BIT(ERROR) | BIT(SLUB_DEBUG);
 	}
 
-	/* PG_reclaim is overloaded as PG_readahead in the read path */
-	if ((flags & (BIT(RECLAIM) | BIT(WRITEBACK))) == BIT(RECLAIM))
-		flags ^= BIT(RECLAIM) | BIT(READAHEAD);
-
 	if (pme & PM_SOFT_DIRTY)
 		flags |= BIT(SOFTDIRTY);
 	if (pme & PM_FILE)
-- 
2.45.2