From: Matthew Wilcox > From: Rasmus Villemoes [mailto:linux@xxxxxxxxxxxxxxxxxx] > > This sounds good. I think there may still be a lot of users that never > > allocate more than a handful of IDAs, making a 128 byte allocation still > > somewhat excessive. One thing I considered was (exactly as it's done for > > file descriptor tables) to embed a single word in the struct ida and > > use that initially; I haven't looked closely at newIDA, so I don't know > > how easy that would be or if its worth the complexity. > > Heh, I was thinking about that too. The radix tree supports "exceptional > entries" which have the bottom bit set. On a 64-bit machine, we could use 62 > of the bits in the radix tree root to store the ID bitmap. I'm a little wary of the > potential complexity, but we should try it out. Test patch here: http://git.infradead.org/users/willy/linux-dax.git/shortlog/refs/heads/idr-2016-12-16 It passes the test suite ... which I actually had to adjust because it now succeeds in cases where it hadn't (allocating ID 0 without preallocating), and it will now fail in cases where it hadn't previously (assuming a single preallocation would be enough). There shouldn't be any examples of that in the kernel proper; it was simply me being lazy when I wrote the test suite. ��.n��������+%������w��{.n�����{����n�r������&��z�ޗ�zf���h���~����������_��+v���)ߣ�
