Messages in this thread | | | Date | Thu, 31 Jan 2002 09:46:52 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH] Radix-tree pagecache for 2.5 |
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On Thu, 31 Jan 2002, Andrea Arcangeli wrote: > > but with the radix tree (please correct me if I'm wrong) the height will > increase eventually, no matter what (so it won't be an effective O(1) > like the hashtable provides in real life, not the worst case, the common > case). With the hashtable the height won't increase instead.
No.
The radix tree is basically O(1), because the maximum depth of a 7-bit radix tree is just 5. The index is only a 32-bit number.
We could, in fact, make all page caches use a fixed-depth tree, which is clearly O(1). But the radix tree is slightly faster and tends to use less memory under common loads, so..
Remember: you must NOT ignore the constant part of a "O(x)" equation. Hashes tend to be effectively O(1) under most loads, but they have cache costs, and they have scalability costs that a radix tree doesn't have.
Linus
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