> When you use blocks in LIFO (stack) order, the back of the list gets
> clogged up with blocks that don't get used and don't get combined,
> either. Because no neighbours want to combine with them, allocating
> them doesn't block any defragmentation, so they're the best blocks to
> put to use. But instead a few blocks at the head of the list get all
> the traffic.
while FIFO is usually better for caching, it has a hidden effect on SMP,
freshly freed and reallocated dirty pages might generate cross-CPU cache
invalidation traffic if a page shows up on 'another' CPU. If they are
LIFO, dirty cachelines get clean in a 'natural' way, by getting kicked out
of the LRU scheme sometime. (possibly giving a more effective way of
writeback, instead of the forced writeback)
so LIFO might even end up performing better on SMP, when compared to the
current allocator.
(although there is a better way to solve this on SMP, by doing per-CPU
freelists, but anyway)
-- mingo
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