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authorDave Hansen <dave.hansen@linux.intel.com>2021-02-24 12:09:15 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2021-02-24 13:38:34 -0800
commit519983645a9f2ec339cabfa0c6ef7b09be985dd0 (patch)
treeee4826a7b99abb77c5b99f3cb8f82671cf4f144b /mm
parentff5461176213d5fd5cfb7e981f9add4d856e415a (diff)
mm/vmscan: restore zone_reclaim_mode ABI
I went to go add a new RECLAIM_* mode for the zone_reclaim_mode sysctl. Like a good kernel developer, I also went to go update the documentation. I noticed that the bits in the documentation didn't match the bits in the #defines. The VM never explicitly checks the RECLAIM_ZONE bit. The bit is, however implicitly checked when checking 'node_reclaim_mode==0'. The RECLAIM_ZONE #define was removed in a cleanup. That, by itself is fine. But, when the bit was removed (bit 0) the _other_ bit locations also got changed. That's not OK because the bit values are documented to mean one specific thing. Users surely do not expect the meaning to change from kernel to kernel. The end result is that if someone had a script that did: sysctl vm.zone_reclaim_mode=1 it would have gone from enabling node reclaim for clean unmapped pages to writing out pages during node reclaim after the commit in question. That's not great. Put the bits back the way they were and add a comment so something like this is a bit harder to do again. Update the documentation to make it clear that the first bit is ignored. Link: https://lkml.kernel.org/r/20210219172555.FF0CDF23@viggo.jf.intel.com Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") Reviewed-by: Ben Widawsky <ben.widawsky@intel.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Christoph Lameter <cl@linux.com> Cc: Alex Shi <alex.shi@linux.alibaba.com> Cc: Daniel Wagner <dwagner@suse.de> Cc: "Tobin C. Harding" <tobin@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Huang Ying <ying.huang@intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Qian Cai <cai@lca.pw> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/vmscan.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index fea6b43bc1f9..562e87cbd7a1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4085,8 +4085,13 @@ module_init(kswapd_init)
*/
int node_reclaim_mode __read_mostly;
-#define RECLAIM_WRITE (1<<0) /* Writeout pages during reclaim */
-#define RECLAIM_UNMAP (1<<1) /* Unmap pages during reclaim */
+/*
+ * These bit locations are exposed in the vm.zone_reclaim_mode sysctl
+ * ABI. New bits are OK, but existing bits can never change.
+ */
+#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
+#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
+#define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */
/*
* Priority for NODE_RECLAIM. This determines the fraction of pages