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Date:   Fri, 14 Apr 2023 13:26:10 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc:     "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] mm/mmap: Regression fix for unmapped_area{_topdown}
Message-ID: <20230414172610.f35pngvz6cilxsdq@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
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        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20230414145728.4067069-1-Liam.Howlett@oracle.com>
 <20230414145728.4067069-3-Liam.Howlett@oracle.com>
 <3bf69efaeddae3599a6d7ea8a225f64066811473.camel@intel.com>
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* Edgecombe, Rick P <rick.p.edgecombe@intel.com> [230414 12:27]:
> On Fri, 2023-04-14 at 10:57 -0400, Liam R. Howlett wrote:<br>
> > +=A0=A0=A0=A0=A0=A0=A0tmp =3D mas_next(&mas, ULONG_MAX);
> > +=A0=A0=A0=A0=A0=A0=A0if (tmp && (tmp->vm_flags & VM_GROWSDOWN)) {
>=20
> Why also check VM_GROWSDOWN here (and VM_GROWSUP below)?
> vm_start/end_gap() already have checks inside.

An artifact of a plan that was later abandoned.

>=20
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0if (vm_start_gap(tmp) < g=
ap + length - 1) {
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0l=
ow_limit =3D tmp->vm_end;
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0m=
as_reset(&mas);
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0g=
oto retry;
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0}
> > +=A0=A0=A0=A0=A0=A0=A0} else {
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0tmp =3D mas_prev(&mas, 0)=
;
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0if (tmp && (tmp->vm_flags=
 & VM_GROWSUP) &&
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 vm_end_gap(tmp)=
 > gap) {
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0l=
ow_limit =3D vm_end_gap(tmp);=20
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0m=
as_reset(&mas);
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0g=
oto retry;=20
> > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0}
> > +=A0=A0=A0=A0=A0=A0=A0}=20
> > +
>=20
> Could it be like this?

Yes, I'll make this change.  Thanks for the suggestion.

>=20
> tmp =3D mas_next(&mas, ULONG_MAX);
> if (tmp && vm_start_gap(tmp) < gap + length - 1) {
> 		low_limit =3D tmp->vm_end;
> 		mas_reset(&mas);
> 		goto retry;
> 	}
> } else {
> 	tmp =3D mas_prev(&mas, 0);
> 	if (tmp && vm_end_gap(tmp) > gap) {
> 		low_limit =3D vm_end_gap(tmp);
> 		mas_reset(&mas);
> 		goto retry;
> 	}
> }
>=20