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