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From:   Michael Kelley <mikelley@microsoft.com>
To:     "lantianyu1986@gmail.com" <lantianyu1986@gmail.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
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Subject: RE: [RFC PATCH V2 1/10] mm/resource: Move child to new resource when
 release mem region.
Thread-Topic: [RFC PATCH V2 1/10] mm/resource: Move child to new resource when
 release mem region.
Thread-Index: AQHVxVvKIEcG+CpTJkitsskMuv0x06fz8zSA
Date:   Mon, 20 Jan 2020 18:34:00 +0000
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 <20200107130950.2983-2-Tianyu.Lan@microsoft.com>
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From: Tianyu Lan <Tianyu.Lan@microsoft.com> Sent: Tuesday, January 7, 2020 =
5:10 AM
>=20
> When release mem region, old mem region may be splited to
> two regions. Current allocate new struct resource for high
> end mem region but not move child resources whose ranges are
> in the high end range to new resource. When adjust old mem
> region's range, adjust_resource() detects child region's range
> is out of new range and return error. Move child resources to
> high end resource before adjusting old mem range.
>=20
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
>  kernel/resource.c | 38 ++++++++++++++++++++++++++++++++++----
>  1 file changed, 34 insertions(+), 4 deletions(-)
>=20
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 76036a41143b..1c7362825134 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -181,6 +181,38 @@ static struct resource *alloc_resource(gfp_t flags)
>  	return res;
>  }
>=20
> +static void move_child_to_newresource(struct resource *old,
> +				      struct resource *new)
> +{
> +	struct resource *tmp, **p, **np;
> +
> +	if (!old->child)
> +		return;

I don't think the above test is needed.  This case is handled by the first
three lines of the "for" loop.

> +
> +	p =3D &old->child;
> +	np =3D &new->child;
> +
> +	for (;;) {
> +		tmp =3D *p;
> +		if (!tmp)
> +			break;
> +
> +		if (tmp->start >=3D new->start && tmp->end <=3D new->end) {
> +			tmp->parent =3D new;
> +			*np =3D tmp;
> +			np =3D &tmp->sibling;
> +			*p =3D tmp->sibling;
> +
> +			if (!tmp->sibling)
> +				*np =3D NULL;

I don't think the above two lines are right.  They seem tautological.  If t=
he ! were
removed it would be clearing the sibling link for the child as it exists un=
der its new
parent, which should be done.  But the child that is moved to the new paren=
t always
becomes the last entry in the new parent's child list.  So could you just u=
nconditionally
do tmp->sibling =3D NULL?   That link will get fixed up if another child is=
 moved.

Michael

> +			continue;
> +		}
> +
> +		p =3D &tmp->sibling;
> +	}
> +}
> +
> +
>  /* Return the conflict entry if you can't request it */
>  static struct resource * __request_resource(struct resource *root, struc=
t resource *new)
>  {
> @@ -1246,9 +1278,6 @@ EXPORT_SYMBOL(__release_region);
>   * Note:
>   * - Additional release conditions, such as overlapping region, can be
>   *   supported after they are confirmed as valid cases.
> - * - When a busy memory resource gets split into two entries, the code
> - *   assumes that all children remain in the lower address entry for
> - *   simplicity.  Enhance this logic when necessary.
>   */
>  int release_mem_region_adjustable(struct resource *parent,
>  				  resource_size_t start, resource_size_t size)
> @@ -1331,11 +1360,12 @@ int release_mem_region_adjustable(struct resource=
 *parent,
>  			new_res->sibling =3D res->sibling;
>  			new_res->child =3D NULL;
>=20
> +			move_child_to_newresource(res, new_res);
> +			res->sibling =3D new_res;
>  			ret =3D __adjust_resource(res, res->start,
>  						start - res->start);
>  			if (ret)
>  				break;
> -			res->sibling =3D new_res;
>  			new_res =3D NULL;
>  		}
>=20
> --
> 2.14.5