linux-kernel - Re: [PATCH RFC v2 13/18] dax/bus: Factor out dev dax resize logic

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Message-ID: <64f7fc36a911a_1e8e78294b9@iweiny-mobl.notmuch>
Date:   Tue, 5 Sep 2023 21:12:38 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        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

Jonathan Cameron wrote:
> 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>

Thanks!

> 
> 
> > ---
> >  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.

Done.

> 
> > + * 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

That is because my brain has a real consistency issue on this...  ;-)

'.' removed.

Thanks again,
Ira