[061/143] mm/vmscan: replace implicit RECLAIM_ZONE checks with explicit checks

Commit Message

Andrew Morton May 5, 2021, 1:36 a.m. UTC

From: Dave Hansen <[e-mail]>
Subject: mm/vmscan: replace implicit RECLAIM_ZONE checks with explicit checks

RECLAIM_ZONE was assumed to be unused because it was never explicitly used
in the kernel.  However, there were a number of places where it was
checked implicitly by checking 'node_reclaim_mode' for a zero value.

These zero checks are not great because it is not obvious what a zero mode
*means* in the code.  Replace them with a helper which makes it more
obvious: node_reclaim_enabled().

This helper also provides a handy place to explicitly check the
RECLAIM_ZONE bit itself.  Check it explicitly there to make it more
obvious where the bit can affect behavior.

This should have no functional impact.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Dave Hansen <[e-mail]>
Reviewed-by: Ben Widawsky <[e-mail]>
Reviewed-by: Oscar Salvador <[e-mail]>
Acked-by: Christoph Lameter <[e-mail]>
Acked-by: David Rientjes <[e-mail]>
Cc: Alex Shi <[e-mail]>
Cc: "Tobin C. Harding" <[e-mail]>
Cc: Huang Ying <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Qian Cai <[e-mail]>
Cc: Daniel Wagner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/swap.h |    7 +++++++
 mm/khugepaged.c      |    2 +-
 mm/page_alloc.c      |    2 +-
 3 files changed, 9 insertions(+), 2 deletions(-)

Patch

--- a/include/linux/swap.h~mm-vmscan-replace-implicit-reclaim_zone-checks-with-explicit-checks
+++ a/include/linux/swap.h
@@ -12,6 +12,7 @@ 
 #include <linux/fs.h>
 #include <linux/atomic.h>
 #include <linux/page-flags.h>
+#include <uapi/linux/mempolicy.h>
 #include <asm/page.h>
 
 struct notifier_block;
@@ -378,6 +379,12 @@  extern int sysctl_min_slab_ratio;
 #define node_reclaim_mode 0
 #endif
 
+static inline bool node_reclaim_enabled(void)
+{
+	/* Is any node_reclaim_mode bit set? */
+	return node_reclaim_mode & (RECLAIM_ZONE|RECLAIM_WRITE|RECLAIM_UNMAP);
+}
+
 extern void check_move_unevictable_pages(struct pagevec *pvec);
 
 extern int kswapd_run(int nid);
--- a/mm/khugepaged.c~mm-vmscan-replace-implicit-reclaim_zone-checks-with-explicit-checks
+++ a/mm/khugepaged.c
@@ -809,7 +809,7 @@  static bool khugepaged_scan_abort(int ni
 	 * If node_reclaim_mode is disabled, then no extra effort is made to
 	 * allocate memory locally.
 	 */
-	if (!node_reclaim_mode)
+	if (!node_reclaim_enabled())
 		return false;
 
 	/* If there is a count for this node already, it must be acceptable */
--- a/mm/page_alloc.c~mm-vmscan-replace-implicit-reclaim_zone-checks-with-explicit-checks
+++ a/mm/page_alloc.c
@@ -3968,7 +3968,7 @@  retry:
 			if (alloc_flags & ALLOC_NO_WATERMARKS)
 				goto try_this_zone;
 
-			if (node_reclaim_mode == 0 ||
+			if (!node_reclaim_enabled() ||
 			    !zone_allows_reclaim(ac->preferred_zoneref->zone, zone))
 				continue;