On Wed, 2013-04-10 at 14:44 -0700, Andrew Morton wrote:
> On Wed, 10 Apr 2013 11:17:00 -0600 Toshi Kani <toshi.kani@xxxxxx> wrote:
>
> > Added release_mem_region_adjustable(), which releases a requested
> > region from a currently busy memory resource. This interface
> > adjusts the matched memory resource accordingly even if the
> > requested region does not match exactly but still fits into.
> >
> > This new interface is intended for memory hot-delete. During
> > bootup, memory resources are inserted from the boot descriptor
> > table, such as EFI Memory Table and e820. Each memory resource
> > entry usually covers the whole contigous memory range. Memory
> > hot-delete request, on the other hand, may target to a particular
> > range of memory resource, and its size can be much smaller than
> > the whole contiguous memory. Since the existing release interfaces
> > like __release_region() require a requested region to be exactly
> > matched to a resource entry, they do not allow a partial resource
> > to be released.
> >
> > This new interface is restrictive (i.e. release under certain
> > conditions), which is consistent with other release interfaces,
> > __release_region() and __release_resource(). Additional release
> > conditions, such as an overlapping region to a resource entry,
> > can be supported after they are confirmed as valid cases.
> >
> > There is no change to the existing interfaces since their restriction
> > is valid for I/O resources.
> >
> > ...
> >
> > +int release_mem_region_adjustable(struct resource *parent,
> > + resource_size_t start, resource_size_t size)
> > +{
> > + struct resource **p;
> > + struct resource *res, *new;
> > + resource_size_t end;
> > + int ret = -EINVAL;
> > +
> > + end = start + size - 1;
> > + if ((start < parent->start) || (end > parent->end))
> > + return ret;
> > +
> > + p = &parent->child;
> > + write_lock(&resource_lock);
> > +
> > + while ((res = *p)) {
> > + if (res->start >= end)
> > + break;
> > +
> > + /* look for the next resource if it does not fit into */
> > + if (res->start > start || res->end < end) {
> > + p = &res->sibling;
> > + continue;
> > + }
> > +
> > + if (!(res->flags & IORESOURCE_MEM))
> > + break;
> > +
> > + if (!(res->flags & IORESOURCE_BUSY)) {
> > + p = &res->child;
> > + continue;
> > + }
> > +
> > + /* found the target resource; let's adjust accordingly */
> > + if (res->start == start && res->end == end) {
> > + /* free the whole entry */
> > + *p = res->sibling;
> > + kfree(res);
> > + ret = 0;
> > + } else if (res->start == start && res->end != end) {
> > + /* adjust the start */
> > + ret = __adjust_resource(res, end + 1,
> > + res->end - end);
> > + } else if (res->start != start && res->end == end) {
> > + /* adjust the end */
> > + ret = __adjust_resource(res, res->start,
> > + start - res->start);
> > + } else {
> > + /* split into two entries */
> > + new = kzalloc(sizeof(struct resource), GFP_KERNEL);
>
> Nope, we can't perform a GFP_KERNEL allocation under write_lock().
>
> Was this code path runtime tested? If no, please try
> to find a way to test it. If yes, please see
> Documentation/SubmitChecklist section 12 and use that in the future.
Yes, I tested all cases. But I did not test with all the config options
described in the document. I will make sure to test with the options
next time. Thanks a lot for the pointer!
> I'll switch it to GFP_ATOMIC. Which is horridly lame but the
> allocation is small and alternatives are unobvious.
Great! Again, thanks for the update!
-Toshi
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