On Thu, Jan 27, 2022 at 11:09:44AM +0100, Eugenio Perez Martin wrote:
> > > +/**
> > > + * Try to accomodate a map of size ret->size in a hole between
> > > + * max(end(hole_left), iova_start).
> >
> > I think this functions need the most comments, and above sentence is more or
> > less not sounding correct... My try...
> >
> > /*
> > * Try to find an unallocated IOVA range between LEFT and RIGHT elements.
> > *
> > * There're three cases:
> > *
> > * (1) When LEFT==NULL, RIGHT must be non-NULL and it means we're iterating at
> > * the 1st element.
> > *
> > * (2) When RIGHT==NULL, LEFT must be non-NULL and it means we're iterating at
> > * the last element.
> > *
> > * (3) When both LEFT and RIGHT are non-NULL, this is the most common case,
> > * we'll try to find a hole between LEFT and RIGHT mapping.
> > */
> >
>
> This is also called with left == NULL and right == NULL in the first
> allocation with an empty tree. This allows iova_tree_alloc to have the
> same code path both if the three is empty or not.
>
> But I can add the use cases in the doc for sure.
Ah, right.
>
> > > + *
> > > + * @args Arguments to allocation
> > > + */
> > > +static bool iova_tree_alloc_map_in_hole(const struct IOVATreeAllocArgs *args)
> > > +{
> > > + const DMAMap *left = args->hole_left, *right = args->hole_right;
> > > + uint64_t hole_start, hole_last;
> > > +
> > > + if (right && right->iova + right->size < args->iova_begin) {
> > > + return false;
> > > + }
> > > +
> > > + if (left && left->iova > args->iova_last) {
> > > + return false;
> > > + }
> > > +
> > > + hole_start = MAX(left ? left->iova + left->size + 1 : 0, args->iova_begin);
> > > + hole_last = MIN(right ? right->iova : HWADDR_MAX, args->iova_last);
> >
> > I assume these values should be always inclusive, hence
> >
> > s/right->iova/right->iova + 1/
> >
> > ?
> >
>
> Right, it is confusing the way it's written. But I think it should be
> right->iova - 1 in any case to make it the hole last element, isn't
> it?
I was thinking "-1" but I failed to make it coherent with the thought when
typing.. Heh.
>
> Would it work better to rename variable hole_last to hole_end? If not,
> we have a special case of the second allocation when iova_begin == 0:
> - We successfully allocate a DMAMap of size N. By the way the
> algorithm works, it starts at 0, so [0, N] is allocated.
If we're always talking about inclusive ranges, shouldn't it be [0, N-1]?
> - We try to allocate a second one of size M. At the first iteration,
> "right" is the previously allocated DMAMap.
> Using the -1 trick we get hole_end == HWADDR_MAX.
I'm not sure I get the point, but both naming look fine to me. As long as we
use inclusive ranges, then hole_end/last will be limited to HWADDR_MAX.
> > > +static gboolean iova_tree_alloc_traverse(gpointer key, gpointer value,
> > > + gpointer pargs)
> > > +{
> > > + struct IOVATreeAllocArgs *args = pargs;
> > > + DMAMap *node = value;
> > > +
> > > + assert(key == value);
> > > +
> > > + iova_tree_alloc_args_iterate(args, node);
> > > + if (args->hole_left && args->hole_left->iova > args->iova_last) {
> >
> > IMHO this check is redundant and can be dropped, as it's already done in
> > iova_tree_alloc_map_in_hole().
> >
>
> Assuming we add "iova_found" to iova_tree_alloc_map_in_hole to
> IOVATreeAllocArgs as you propose, it returns true if we are able to
> allocate a DMAMap entry, so no more iterations are needed. But if it
> returns false, it simply means that DMAMap cannot be allocated between
> left (or iova_begin) and right (iova_end). It doesn't tell if you can
> keep iterating or not. In other words, false == keep iterating if you
> can.
>
> This other check signals the end of the available hole, and to avoid
> iterating beyond iova_last in the (unlikely?) case we have more nodes
> to iterate beyond that.
>
> I'll try to make it more explicit.
Makes sense. Comment works.
Thanks,
--
Peter Xu
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