[PATCH v2 18/26] mm/fbatch: remove lru_add_drain() and _all() calls from various

[Hugh Dickins <hughd@google.com>]

Splitting into little patches gets tedious: now that folios on per-cpu
fbatches no longer hold an extra reference (and have the lru flag set),
most calls to lru_add_drain(), and more importantly lru_add_drain_all(),
should be removed.

Remove lru_add_drain() from compact_zone().
Remove lru_add_drain_all() from compact_nodes() and compact_store().
Keep lru_add_drain_cpu_zone() in compact_zone(): it was always a bit of
a hack, a cheap way to get a local_lock() around pcp drain_pages_zone().

Remove lru_add_drain() and lru_add_drain_all() from generic_fadvise(
POSIX_FADV_DONTNEED), but still retry once on failure; remove outdated
comment line from mapping_try_invalidate().

Remove every lru_add_drain() and lru_add_drain_all() from khugepaged.c.

Remove lru_add_drain_all() from KSM's scan_get_next_rmap_item() restart.

Remove lru_add_drain() from wp_can_reuse_anon_folio() and do_swap_page().

Remove lru_add_drain(), lru_add_drain_all() from migrate_device_unmap().

Keep lru_add_drain()s in mm/gup.c populate_vma_page_range() and
faultin_page_range(): good housekeeping after a bulk operation.

Keep lru_add_drain()s in mm/madvise.c: the ones after a bulk op probably
do want to "Push any new pages onto the LRU now", and update the stats;
the ones before a bulk op may be trying to stabilize initial conditions,
or to minimize draining under ptlock.

Keep lru_add_drain_all() in memcg-v1's mem_cgroup_force_empty():
it probably does want to push onto the LRU and update the stats.

Keep lru_add_drain() after bulk op in mlock_vma_pages_range(), partly
for "Unevictable kB" accuracy; but remove the lru_add_drain() before it.

Keep lru_add_drain()s in swap_cluster_readahead(), swap_vma_readahead():
they do want to "Push any new pages onto the LRU now" (akpm 2.5.46).

Keep lru_add_drain()s and lru_add_drain_all() throughout mm/vmscan.c:
it works on LRUs, so it does need folios to be on an actual LRU.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 mm/compaction.c     | 12 +-----------
 mm/fadvise.c        | 17 +----------------
 mm/khugepaged.c     | 11 -----------
 mm/ksm.c            | 12 ------------
 mm/memory.c         | 14 ++------------
 mm/migrate_device.c |  9 ---------
 mm/mlock.c          |  1 -
 mm/truncate.c       |  1 -
 8 files changed, 4 insertions(+), 73 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 1290b9170cb2..5944094253b0 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2652,9 +2652,6 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 
 	trace_mm_compaction_begin(cc, start_pfn, end_pfn, sync);
 
-	/* lru_add_drain_all could be expensive with involving other CPUs */
-	lru_add_drain();
-
 	while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
 		int err;
 		unsigned long iteration_start_pfn = cc->migrate_pfn;
@@ -2969,9 +2966,6 @@ static int compact_nodes(void)
 {
 	int ret, nid;
 
-	/* Flush pending updates to the LRU lists */
-	lru_add_drain_all();
-
 	for_each_online_node(nid) {
 		ret = compact_node(NODE_DATA(nid), false);
 		if (ret)
@@ -3036,12 +3030,8 @@ static ssize_t compact_store(struct device *dev,
 {
 	int nid = dev->id;
 
-	if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
-		/* Flush pending updates to the LRU lists */
-		lru_add_drain_all();
-
+	if (nid >= 0 && nid < nr_node_ids && node_online(nid))
 		compact_node(NODE_DATA(nid), false);
-	}
 
 	return count;
 }
diff --git a/mm/fadvise.c b/mm/fadvise.c
index b63fe21416ff..f788a5020384 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -143,27 +143,12 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		if (end_index >= start_index) {
 			unsigned long nr_failed = 0;
 
-			/*
-			 * It's common to FADV_DONTNEED right after
-			 * the read or write that instantiates the
-			 * pages, in which case there will be some
-			 * sitting on the local LRU cache. Try to
-			 * avoid the expensive remote drain and the
-			 * second cache tree walk below by flushing
-			 * them out right away.
-			 */
-			lru_add_drain();
-
 			mapping_try_invalidate(mapping, start_index, end_index,
 					&nr_failed);
-
 			/*
-			 * The failures may be due to the folio being
-			 * in the LRU cache of a remote CPU. Drain all
-			 * caches and try again.
+			 * Retry if any failures, in case they were transient.
 			 */
 			if (nr_failed) {
-				lru_add_drain_all();
 				invalidate_mapping_pages(mapping, start_index,
 						end_index);
 			}
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 75639298efc2..d09f848d3591 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1236,10 +1236,6 @@ static enum scan_result __collapse_huge_page_swapin(struct mm_struct *mm,
 	if (pte)
 		pte_unmap(pte);
 
-	/* Drain LRU cache to remove extra pin on the swapped in pages */
-	if (swapped_in)
-		lru_add_drain();
-
 	result = SCAN_SUCCEED;
 out:
 	trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, result,
@@ -2320,8 +2316,6 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 					result = SCAN_FAIL;
 					goto xa_unlocked;
 				}
-				/* drain lru cache to help folio_isolate_lru() */
-				lru_add_drain();
 			} else if (folio_trylock(folio)) {
 				folio_get(folio);
 				xas_unlock_irq(&xas);
@@ -2335,8 +2329,6 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 				page_cache_sync_readahead(mapping, &file->f_ra,
 							  file, index,
 							  end - index);
-				/* drain lru cache to help folio_isolate_lru() */
-				lru_add_drain();
 				folio = filemap_lock_folio(mapping, index);
 				if (IS_ERR(folio)) {
 					result = SCAN_FAIL;
@@ -2975,8 +2967,6 @@ static void khugepaged_do_scan(struct collapse_control *cc)
 	bool wait = true;
 	enum scan_result result = SCAN_SUCCEED;
 
-	lru_add_drain_all();
-
 	cc->progress = 0;
 	while (true) {
 		cond_resched();
@@ -3208,7 +3198,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
 	cc->progress = 0;
 
 	mmgrab(mm);
-	lru_add_drain_all();
 
 	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
 		enum scan_result result = SCAN_FAIL;
diff --git a/mm/ksm.c b/mm/ksm.c
index 49d48d1e0998..890e2c51106d 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2625,18 +2625,6 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 		advisor_start_scan();
 		trace_ksm_start_scan(ksm_scan.seqnr, ksm_rmap_items);
 
-		/*
-		 * A number of pages can hang around indefinitely in per-cpu
-		 * LRU cache, raised page count preventing write_protect_page
-		 * from merging them.  Though it doesn't really matter much,
-		 * it is puzzling to see some stuck in pages_volatile until
-		 * other activity jostles them out, and they also prevented
-		 * LTP's KSM test from succeeding deterministically; so drain
-		 * them here (here rather than on entry to ksm_do_scan(),
-		 * so we don't IPI too often when pages_to_scan is set low).
-		 */
-		lru_add_drain_all();
-
 		/*
 		 * Whereas stale stable_nodes on the stable_tree itself
 		 * get pruned in the regular course of stable_tree_search(),
diff --git a/mm/memory.c b/mm/memory.c
index 8b0c2c735d3d..e9e2199ba5e9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4313,9 +4313,6 @@ static bool __wp_can_reuse_large_anon_folio(struct folio *folio,
 static bool wp_can_reuse_anon_folio(struct folio *folio,
 				    struct vm_area_struct *vma)
 {
-	const bool maybe_in_lru_cache = !folio_test_lru(folio);
-	const bool in_swapcache = folio_test_swapcache(folio);
-
 	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && folio_test_large(folio))
 		return __wp_can_reuse_large_anon_folio(folio, vma);
 
@@ -4326,16 +4323,9 @@ static bool wp_can_reuse_anon_folio(struct folio *folio,
 	 *
 	 * KSM doesn't necessarily raise the folio refcount.
 	 */
-	if (folio_test_ksm(folio) ||
-	    folio_ref_count(folio) > 1 + maybe_in_lru_cache + in_swapcache)
+	if (folio_test_ksm(folio))
 		return false;
-	if (maybe_in_lru_cache)
-		/*
-		 * We cannot easily detect+handle references from
-		 * remote LRU caches or references to LRU folios.
-		 */
-		lru_add_drain();
-	if (folio_ref_count(folio) > 1 + in_swapcache)
+	if (folio_ref_count(folio) > 1 + folio_test_swapcache(folio))
 		return false;
 	if (!folio_trylock(folio))
 		return false;
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 009bfa8b212d..7ece4ca0654a 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -575,11 +575,8 @@ static unsigned long migrate_device_unmap(unsigned long *src_pfns,
 	struct folio *fault_folio = fault_page ?
 		page_folio(fault_page) : NULL;
 	unsigned long i, restore = 0;
-	bool allow_drain = true;
 	unsigned long unmapped = 0;
 
-	lru_add_drain();
-
 	for (i = 0; i < npages; ) {
 		struct page *page = migrate_pfn_to_page(src_pfns[i]);
 		struct folio *folio;
@@ -600,12 +597,6 @@ static unsigned long migrate_device_unmap(unsigned long *src_pfns,
 
 		/* ZONE_DEVICE folios are not on LRU */
 		if (!folio_is_zone_device(folio)) {
-			if (!folio_test_lru(folio) && allow_drain) {
-				/* Drain CPU's lru cache */
-				lru_add_drain_all();
-				allow_drain = false;
-			}
-
 			if (!folio_isolate_lru(folio)) {
 				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
 				restore++;
diff --git a/mm/mlock.c b/mm/mlock.c
index 97134eff6b56..971430e6251e 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -424,7 +424,6 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
 	vma_start_write(vma);
 	vma_flags_reset_once(vma, new_vma_flags);
 
-	lru_add_drain();
 	walk_page_range_vma(vma, start, end, &mlock_walk_ops, NULL);
 	lru_add_drain();
 
diff --git a/mm/truncate.c b/mm/truncate.c
index 4151f7a167e3..7ea5d513f76a 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -571,7 +571,6 @@ unsigned long mapping_try_invalidate(struct address_space *mapping,
 			 */
 			if (!ret) {
 				deactivate_file_folio(folio);
-				/* Likely in the lru cache of a remote CPU */
 				if (nr_failed)
 					(*nr_failed)++;
 			}
-- 
2.51.0