From: Dave Hansen <[email protected]>
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.
Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Ben Widawsky <[email protected]>
Cc: Alex Shi <[email protected]>
Cc: "Tobin C. Harding" <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Qian Cai <[email protected]>
Cc: Daniel Wagner <[email protected]>
--
Note: This is not cc'd to stable. It does not fix any bugs.
---
b/include/linux/swap.h | 7 +++++++
b/mm/khugepaged.c | 2 +-
b/mm/page_alloc.c | 2 +-
3 files changed, 9 insertions(+), 2 deletions(-)
diff -puN include/linux/swap.h~mm-vmscan-node_reclaim_mode_helper include/linux/swap.h
--- a/include/linux/swap.h~mm-vmscan-node_reclaim_mode_helper 2020-10-06 13:39:22.850818437 -0700
+++ b/include/linux/swap.h 2020-10-06 13:39:22.859818437 -0700
@@ -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;
@@ -381,6 +382,12 @@ 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);
diff -puN mm/khugepaged.c~mm-vmscan-node_reclaim_mode_helper mm/khugepaged.c
--- a/mm/khugepaged.c~mm-vmscan-node_reclaim_mode_helper 2020-10-06 13:39:22.852818437 -0700
+++ b/mm/khugepaged.c 2020-10-06 13:39:22.859818437 -0700
@@ -794,7 +794,7 @@ 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 */
diff -puN mm/page_alloc.c~mm-vmscan-node_reclaim_mode_helper mm/page_alloc.c
--- a/mm/page_alloc.c~mm-vmscan-node_reclaim_mode_helper 2020-10-06 13:39:22.855818437 -0700
+++ b/mm/page_alloc.c 2020-10-06 13:39:22.862818437 -0700
@@ -3802,7 +3802,7 @@ 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;
_
On Tue, 6 Oct 2020, Dave Hansen wrote:
> 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().
Well it uselessly checks bits. But whatever. It will prevent future code
removal.
Acked-by: Christoph Lameter <[email protected]>