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Message-ID: <20230830122741.00007628@Huawei.com>
Date: Wed, 30 Aug 2023 12:27:41 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Ira Weiny <ira.weiny@...el.com>
CC: Dan Williams <dan.j.williams@...el.com>,
Navneet Singh <navneet.singh@...el.com>,
Fan Ni <fan.ni@...sung.com>,
Davidlohr Bueso <dave@...olabs.net>,
Dave Jiang <dave.jiang@...el.com>,
Alison Schofield <alison.schofield@...el.com>,
Vishal Verma <vishal.l.verma@...el.com>,
<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 13/18] dax/bus: Factor out dev dax resize logic
On Mon, 28 Aug 2023 22:21:04 -0700
Ira Weiny <ira.weiny@...el.com> wrote:
> Dynamic Capacity regions must limit dev dax resources to those areas
> which have extents backing real memory. Four alternatives were
> considered to manage the intersection of region space and extents:
>
> 1) Create a single region resource child on region creation which
> reserves the entire region. Then as extents are added punch holes in
> this reservation. This requires new resource manipulation to punch
> the holes and still requires an additional iteration over the extent
> areas which may already have existing dev dax resources used.
>
> 2) Maintain an ordered xarray of extents which can be queried while
> processing the resize logic. The issue is that existing region->res
> children may artificially limit the allocation size sent to
> alloc_dev_dax_range(). IE the resource children can't be directly
> used in the resize logic to find where space in the region is.
>
> 3) Maintain a separate resource tree with extents. This option is the
> same as 2) but with a different data structure. Most ideally we have
> some unified representation of the resource tree.
>
> 4) Create region resource children for each extent. Manage the dax dev
> resize logic in the same way as before but use a region child
> (extent) resource as the parents to find space within each extent.
>
> Option 4 can leverage the existing resize algorithm to find space within
> the extents.
>
> In preparation for this change, factor out the dev_dax_resize logic.
> For static regions use dax_region->res as the parent to find space for
> the dax ranges. Future patches will use the same algorithm with
> individual extent resources as the parent.
>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
Hi Ira,
Some trivial comments on comments, but in general this indeed seems to be doing what you
say and factoring out the static allocation part.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
> drivers/dax/bus.c | 128 +++++++++++++++++++++++++++++++++---------------------
> 1 file changed, 79 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index b76e49813a39..ea7ae82b4687 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -817,11 +817,10 @@ static int devm_register_dax_mapping(struct dev_dax *dev_dax, int range_id)
> return 0;
> }
>
> -static ssize_t dev_dax_resize(struct dax_region *dax_region,
> - struct dev_dax *dev_dax, resource_size_t size)
> +/*
/**
Suitable builds will then check this doc matches the function etc
even if this is never included into any of the docs build.
> + * dev_dax_resize_static - Expand the device into the unused portion of the
> + * region. This may involve adjusting the end of an existing resource, or
> + * allocating a new resource.
> + *
> + * @parent: parent resource to allocate this range in.
> + * @dev_dax: DAX device we are creating this range for
Trivial: Doesn't seem to be consistent on . or not
> + * @to_alloc: amount of space to alloc; must be <= space available in @parent
> + *
> + * Return the amount of space allocated or -ERRNO on failure
> + */
> +static ssize_t dev_dax_resize_static(struct resource *parent,
> + struct dev_dax *dev_dax,
> + resource_size_t to_alloc)
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