tree 9932ecc9ba3010ecc53bdbf5cd299eb0842106ec
parent 7ad3d4d85c7af9632055a6ac0aa15b6b6a321c6b
author Matthew Wilcox <mawilcox@microsoft.com> 1481980697 -0500
committer Matthew Wilcox <mawilcox@microsoft.com> 1487040242 -0500

ida: Use exceptional entries for small IDAs

We can use the root entry as a bitmap and save allocating a 128 byte
bitmap for an IDA that contains only a few entries (30 on a 32-bit
machine, 62 on a 64-bit machine).  This costs about 300 bytes of kernel
text on x86-64, so as long as 3 IDAs fall into this category, this
is a net win for memory consumption.

Thanks to Rasmus Villemoes for his work documenting the problem and
collecting statistics on IDAs.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>