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Subject: Re: [PATCH] maple_tree: use GFP_KERNEL on mas_node_count
Reply-To: jason.sim@samsung.com
Sender: Jaeseon Sim <jason.sim@samsung.com>
From:   Jaeseon Sim <jason.sim@samsung.com>
To:     "Liam R. Howlett" <Liam.Howlett@Oracle.com>
CC:     Matthew Wilcox <willy@infradead.org>,
        Peng Zhang <zhangpeng.00@bytedance.com>,
        "surenb@google.com" <surenb@google.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "jaewon31.kim@gmail.com" <jaewon31.kim@gmail.com>,
        "maple-tree@lists.infradead.org" <maple-tree@lists.infradead.org>,
        Jaewon Kim <jaewon31.kim@samsung.com>
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Date:   Thu, 14 Sep 2023 11:49:37 +0900
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> * Jaeseon Sim <jason.sim=40samsung.com> =5B230907 00:41=5D:
> > > On Thu, Sep 07, 2023 at 12:02:02PM +0800, Peng Zhang wrote:
> > > >=20
> > > >=20
> > > > =E5=9C=A8=202023/9/7=2011:49,=20Matthew=20Wilcox=20=E5=86=99=E9=81=
=93:=0D=0A>=20>=20>=20>=20>=20On=20Thu,=20Sep=2007,=202023=20at=2012:39:14P=
M=20+0900,=20=EC=8B=AC=EC=9E=AC=EC=84=A0=20wrote:=0D=0A>=20>=20>=20>=20>=20=
>=20Use=20GFP_KERNEL=20on=20mas_node_count=20instead=20of=20GFP_NOWAIT=20=
=7C=20__GFP_NOWARN=0D=0A>=20>=20>=20>=20>=20>=20in=20order=20to=20allow=20m=
emory=20reclaim.=0D=0A>=20>=20>=20>=20There=20are=20many=20paths=20that=20c=
all=20maple=20tree's=20mas_node_count().=20Some=20paths=0D=0A>=20>=20>=20>=
=20cannot=20reclaim=20memory.=0D=0A>=20>=20>=20=0D=0A>=20>=20>=20Right=20..=
.=20but=20we=20should=20be=20handling=20the=20ENOMEM=20inside=20the=20maple=
=20tree=20and=0D=0A>=20>=20>=20allocating=20some=20nodes=20with=20GFP_KERNE=
L=20instead=20of=20failing=20fork().=0D=0A>=20>=20>=20=0D=0A>=20>=20>=20>=
=20>=20What=20testing=20did=20you=20do=20of=20this=20patch?=20=20In=20parti=
cular,=20did=20you=20try=20it=0D=0A>=20>=20>=20>=20>=20with=20lockdep=20ena=
bled?=0D=0A>=20>=20I=20did=20power=20on/off=20test=20with=20this=20patch.=
=0D=0A>=20>=20I=20did=20not=20try=20it=20with=20lockdep=20enabled.=0D=0A>=
=20=0D=0A>=20To=20accomplish=20the=20same=20result,=20but=20with=20a=20much=
=20smaller=20scope=20that=20will=0D=0A>=20work=20with=20lockdep,=20I=20woul=
d=20suggest=20changing=20mas_expected_entries()=20to=0D=0A>=20use=20mas_nod=
e_count_gfp()=20(which=20already=20exists)=20and=20pass=20in=20GFP_KERNEL.=
=0D=0A>=20=0D=0A>=20Since=20fork=20is=20the=20only=20current=20user=20of=20=
mas_expected_entries(),=20this=0D=0A>=20won't=20break=20other=20users=20and=
=20we=20can=20deal=20with=20changing=20it=20for=20others=20if=0D=0A>=20it=
=20is=20needed.=0D=0A>=20=0D=0A>=20If=20we=20do=20go=20this=20route,=20plea=
se=20add=20a=20note=20in=20the=20documentation=20about=0D=0A>=20using=20GFP=
_KERNEL.=0D=0A>=20=0D=0A>=20Willy,=20does=20that=20work=20for=20you?=0D=0A>=
=20=0D=0A>=20Thanks,=0D=0A>=20Liam=0D=0A=0D=0ADear=20Liam,=0D=0ACan=20I=20a=
sk=20you=20the=20reason=20why=20mas_node_count=20is=20using=20GFP_NOWAIT=20=
=7C=20__GFP_NOWARN?=0D=0AI=20wonder=20if=20other=20callers=20for=20mas_node=
_count=20might=20have=20similar=20issue.=0D=0A=0D=0AFrom=20your=20opinion,=
=20I'll=20post=20v2=20patch=20as=20follows=0D=0A=0D=0Adiff=20--git=20a/lib/=
maple_tree.c=20b/lib/maple_tree.c=0D=0Aindex=20ee1ff0c59fd7..b0229271c24e=
=20100644=0D=0A---=20a/lib/maple_tree.c=0D=0A+++=20b/lib/maple_tree.c=0D=0A=
=40=40=20-5574,7=20+5574,7=20=40=40=20int=20mas_expected_entries(struct=20m=
a_state=20*mas,=20unsigned=20long=20nr_entries)=0D=0A=20=09/*=20Internal=20=
nodes=20*/=0D=0A=20=09nr_nodes=20+=3D=20DIV_ROUND_UP(nr_nodes,=20nonleaf_ca=
p);=0D=0A=20=09/*=20Add=20working=20room=20for=20split=20(2=20nodes)=20+=20=
new=20parents=20*/=0D=0A-=09mas_node_count(mas,=20nr_nodes=20+=203);=0D=0A+=
=09mas_node_count_gfp(mas,=20nr_nodes=20+=203,=20GFP_KERNEL);=0D=0A=20=0D=
=0A=20=09/*=20Detect=20if=20allocations=20run=20out=20*/=0D=0A=20=09mas->ma=
s_flags=20=7C=3D=20MA_STATE_PREALLOC;=0D=0A--=20=0D=0A2.17.1=0D=0A=0D=0ATha=
nks=0D=0AJaeseon