[PATCH 16/25] mm/fbatch: remove lru_cache_disable(() from NUMA folio migration

Remove lru_cache_disable() from mbind(MOVE), migrate_pages and move_pages
syscall handling. They do not now benefit from lru_add_drain_all() first;
they gain little benefit from invalidating buffer head LRUs first, since
5.0 commit 80409c65e2c6 ("mm: migrate: make buffer_migrate_page_norefs()
actually succeed"); and it's a shame that (even without CAP_SYS_NICE)
they can prevent concurrent tasks from enjoying the use of those caches.

Signed-off-by: Hugh Dickins <[email protected]>
---
 mm/mempolicy.c | 7 -------
 mm/migrate.c   | 3 ---
 2 files changed, 10 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 501e0b80d7da..44912d707d57 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1343,8 +1343,6 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 	long err = 0;
 	nodemask_t tmp;
 
-	lru_cache_disable();
-
 	/*
 	 * Find a 'source' bit set in 'tmp' whose corresponding 'dest'
 	 * bit in 'to' is not also set in 'tmp'.  Clear the found 'source'
@@ -1425,7 +1423,6 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 			break;
 	}
 
-	lru_cache_enable();
 	if (err < 0)
 		return err;
 	return (nr_failed < INT_MAX) ? nr_failed : INT_MAX;
@@ -1530,8 +1527,6 @@ static long do_mbind(unsigned long start, unsigned long len,
 	if (!new)
 		flags |= MPOL_MF_DISCONTIG_OK;
 
-	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
-		lru_cache_disable();
 	{
 		NODEMASK_SCRATCH(scratch);
 		if (scratch) {
@@ -1626,8 +1621,6 @@ static long do_mbind(unsigned long start, unsigned long len,
 		putback_movable_pages(&pagelist);
 mpol_out:
 	mpol_put(new);
-	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
-		lru_cache_enable();
 	return err;
 }
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 534908a0839a..bf9fe533a5fb 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2360,8 +2360,6 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 	int start, i;
 	int err = 0, err1;
 
-	lru_cache_disable();
-
 	for (i = start = 0; i < nr_pages; i++) {
 		const void __user *p;
 		int node;
@@ -2440,7 +2438,6 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 	if (err >= 0)
 		err = err1;
 out:
-	lru_cache_enable();
 	return err;
 }
 
-- 
2.51.0