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From:   Roman Gushchin <guro@fb.com>
To:     Chris Down <chris@chrisdown.name>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
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        Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH] mm: Proportional memory.{low,min} reclaim
Thread-Topic: [PATCH] mm: Proportional memory.{low,min} reclaim
Thread-Index: AQHUs4Zt38UF96mTm0amM4LuPUpLpqXEq9uAgACRwICAAALjgA==
Date:   Mon, 28 Jan 2019 21:52:40 +0000
Message-ID: <20190128215230.GA32069@castle.DHCP.thefacebook.com>
References: <20190124014455.GA6396@chrisdown.name>
 <20190128210031.GA31446@castle.DHCP.thefacebook.com>
 <20190128214213.GB15349@chrisdown.name>
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On Mon, Jan 28, 2019 at 04:42:13PM -0500, Chris Down wrote:
> Roman Gushchin writes:
> > Hm, it looks a bit suspicious to me.
> >=20
> > Let's say memory.low =3D 3G, memory.min =3D 1G and memory.current =3D 2=
G.
> > cgroup_size / protection =3D=3D 1, so scan doesn't depend on memory.min=
 at all.
> >=20
> > So, we need to look directly at memory.emin in memcg_low_reclaim case, =
and
> > ignore memory.(e)low.
>=20
> Hmm, this isn't really a common situation that I'd thought about, but it
> seems reasonable to make the boundaries when in low reclaim to be between
> min and low, rather than 0 and low. I'll add another patch with that. Tha=
nks

It's not a stopper, so I'm perfectly fine with a follow-up patch.

>=20
> > > +			scan =3D clamp(scan, SWAP_CLUSTER_MAX, lruvec_size);
> >=20
> > Idk, how much sense does it have to make it larger than SWAP_CLUSTER_MA=
X,
> > given that it will become 0 on default (and almost any other) priority.
>=20
> In my testing, setting the scan target to 0 and thus reducing scope for
> reclaim can result in increasing the scan priority more than is desirable=
,
> and since we base some vm heuristics based on that, that seemed concernin=
g.
>=20
> I'd rather start being a bit more cautious, erring on the side of scannin=
g
> at least some pages from this memcg when priority gets elevated.
>=20
> Thanks for the review!

For the rest of the patch:
Reviewed-by: Roman Gushchin <guro@fb.com>

Thanks!