Re: [PATCH 4.19 071/114] kernel: sysctl: make drop_caches write-only

From: Sasha Levin
Date: Sun Jan 05 2020 - 10:47:41 EST

On Fri, Jan 03, 2020 at 07:29:11PM +0100, Pavel Machek wrote:

From: Johannes Weiner <hannes@xxxxxxxxxxx>

[ Upstream commit 204cb79ad42f015312a5bbd7012d09c93d9b46fb ]

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.

I have no problem with that, but is it good idea for stable?

Usually I'd drop it, yes. In this case it seems like it made "real"
users interact with the switch incorrectly, which I parse as a bug.

Plus, I seem to recall that drop_caches was somehow dangerous,
debugging-only stuff, one should not use on production system. Did
that get fixed in the meantime?

Sounds like it's being used in production, at scale, so I'd hope so :)