The patch titled
Subject: kernel: sysctl: make drop_caches write-only
has been added to the -mm tree. Its filename is
kernel-sysctl-make-drop_caches-write-only.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kernel-sysctl-make-drop_caches-write-only.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kernel-sysctl-make-drop_caches-write-only.patch
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------------------------------------------------------
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: kernel: sysctl: make drop_caches write-only
Currently, the drop_caches proc file and sysctl read back the last value
written, suggesting this is somehow a stateful setting instead of a
one-time command. Make it write-only, like e.g. compact_memory.
While mitigating a VM problem at scale in our fleet, there was confusion
about whether writing to this file will permanently switch the kernel into
a non-caching mode. This influences the decision making in a tense
situation, where tens of people are trying to fix tens of thousands of
affected machines: Do we need a rollback strategy? What are the
performance implications of operating in a non-caching state for several
days? It also caused confusion when the kernel team said we may need to
write the file several times to make sure it's effective ("But it already
reads back 3?").
Link: http://lkml.kernel.org/r/20191031221602.9375-1-hannes@xxxxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Chris Down <chris@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/sysctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/sysctl.c~kernel-sysctl-make-drop_caches-write-only
+++ a/kernel/sysctl.c
@@ -1466,7 +1466,7 @@ static struct ctl_table vm_table[] = {
.procname = "drop_caches",
.data = &sysctl_drop_caches,
.maxlen = sizeof(int),
- .mode = 0644,
+ .mode = 0200,
.proc_handler = drop_caches_sysctl_handler,
.extra1 = SYSCTL_ONE,
.extra2 = &four,
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
mm-rate-limit-allocation-failure-warnings-more-aggressively.patch
mm-memcontrol-fix-network-errors-from-failing-__gfp_atomic-charges.patch
mm-memcontrol-remove-dead-code-from-memory_max_write.patch
mm-memcontrol-try-harder-to-set-a-new-memoryhigh.patch
mm-drop-mmap_sem-before-calling-balance_dirty_pages-in-write-fault.patch
mm-vmscan-simplify-lruvec_lru_size.patch
mm-clean-up-and-clarify-lruvec-lookup-procedure.patch
mm-vmscan-move-inactive_list_is_low-swap-check-to-the-caller.patch
mm-vmscan-naming-fixes-global_reclaim-and-sane_reclaim.patch
mm-vmscan-replace-shrink_node-loop-with-a-retry-jump.patch
mm-vmscan-turn-shrink_node_memcg-into-shrink_lruvec.patch
mm-vmscan-split-shrink_node-into-node-part-and-memcgs-part.patch
mm-vmscan-split-shrink_node-into-node-part-and-memcgs-part-fix.patch
mm-vmscan-harmonize-writeback-congestion-tracking-for-nodes-memcgs.patch
kernel-sysctl-make-drop_caches-write-only.patch
