Messages in this thread | | | Date | Thu, 01 Sep 2011 17:01:40 -0500 | From | Seth Jennings <> | Subject | Re: [PATCH 0/3] staging: zcache: xcfmalloc support |
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On 09/01/2011 11:54 AM, Dave Hansen wrote: > On Thu, 2011-09-01 at 11:33 -0500, Seth Jennings wrote: >> xcfmalloc is also 0(1) in that the number of freelists >> at that have to be checked is constant and not increasing >> with the number of allocations. The constant hidden >> in the O(1) for finding a suitable block is NUM_FREELISTS. > > The algorithm is technically O(n^2) since there are > XCF_MAX_BLOCKS_PER_ALLOC searches through XCF_NUM_FREELISTS. There's > also the reserved pages refill loop, which is linear too. >
I was seeing n as the number of allocations. Since XCF_MAX_BLOCKS_PER_ALLOC and XCF_NUM_FREELISTS are constant (i.e. not increasing with the number of allocations) wouldn't it be O(1)?
I see it like this:
for (i=0; i<2; i++) { do_something(); }
vs.
do_something(); do_something();
Is one O(n) and the other O(1)? They do the same thing because the loop iterates a constant number of times.
For it to be O(n) it would have to be:
for (i=0; i<n; i++) { do_something(); }
Right?
> xcfmalloc's big compromise is that it doesn't do any searching or > fitting. It might needlessly split larger blocks when two small ones > would have worked, for instance.
Splitting a larger block is the last option. I might not be understanding you correctly, but find_remove_block() does try to find the optimal block to use, which is "searching and fitting" in my mind.
> > -- Dave >
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