[PATCH v4 20/73] idr: Convert to XArray

From: Matthew Wilcox The IDR distinguishes between unallocated entries (read as NULL) and entries where the user has chosen to store NULL. The radix tree was modified to consider NULL entries which had tag 0 _clear_ as being allocated, but it added a lot of complexity.

[PATCH v4 20/73] idr: Convert to XArray

From: Matthew Wilcox The IDR distinguishes between unallocated entries (read as NULL) and entries where the user has chosen to store NULL. The radix tree was modified to consider NULL entries which had tag 0 _clear_ as being allocated, but it added a lot of complexity. Instead, the XArray has