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SubjectRe: [PATCH] make radix tree gang lookup faster by using a bitmap search


On Sun, 28 Aug 2005, James Bottomley wrote:
>
> radix_tree_insert() is reliable from IRQ provided you don't try to use
> radix_tree_preload() and you defined your radix tree gfp flag to be
> GFP_ATOMIC.

It would be better if it wasn't, though.

I really don't see why we made it irq-safe, and take the hit of disabling
interrupts in addition to the locking. That's a quite noticeable loss,
and I don't think it's really a valid thing to insert (or look up) page
cache entries from interrupts.

What _is_ it that makes us do that, btw? Is it just because we clear the
writeback tag bits or something? Sad. It makes page lookup noticeably more
expensive.

Linus
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