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Date:   Fri, 3 Jan 2020 19:29:11 +0100
From:   Pavel Machek <pavel@denx.de>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Johannes Weiner <hannes@cmpxchg.org>,
        Chris Down <chris@chrisdown.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Michal Hocko <mhocko@suse.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <sashal@kernel.org>
Subject: Re: [PATCH 4.19 071/114] kernel: sysctl: make drop_caches write-only
Message-ID: <20200103182911.GE14328@amd>
References: <20200102220029.183913184@linuxfoundation.org>
 <20200102220036.228967185@linuxfoundation.org>
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Hi!

> From: Johannes Weiner <hannes@cmpxchg.org>
>=20
> [ Upstream commit 204cb79ad42f015312a5bbd7012d09c93d9b46fb ]
>=20
> 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?

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?

Best regards,
								Pavel
							=09
> @@ -1411,7 +1411,7 @@ static struct ctl_table vm_table[] =3D {
>  		.procname	=3D "drop_caches",
>  		.data		=3D &sysctl_drop_caches,
>  		.maxlen		=3D sizeof(int),
> -		.mode		=3D 0644,
> +		.mode		=3D 0200,
>  		.proc_handler	=3D drop_caches_sysctl_handler,
>  		.extra1		=3D &one,
>  		.extra2		=3D &four,

--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

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