Re: [PATCH] Radix-tree pagecache for 2.5

[Linus Torvalds]

On Thu, 31 Jan 2002, Andrea Arcangeli wrote:
> >
> > 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.
>
> then it will break on archs with more ram than 1<<(32+PAGE_CACHE_SHIFT).

NO.

The radix tree is an index lookup mechanism.

The index is 32 bits.

That's true regardless of how much RAM you have.

> Also there must be some significant memory overhead that can be
> triggered with a certain layout of pages, in some configuration it
> should take much more ram than the hashtable if I understood well how it
> works.

Considering that the radix tree can _remove_ 8 bytes per "struct page", I
suspect you potentially win more memory than you lose.

		Linus