linux-kernel - Re: [PATCH 0/5] Optimize number of comparisons for heap/heapsort implementaion

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Date: Sun, 21 Jan 2024 11:21:06 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Kuan-Wei Chiu <visitorckw@...il.com>
Cc: colyli@...e.de, bfoster@...hat.com, jserv@...s.ncku.edu.tw, 
	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org
Subject: Re: [PATCH 0/5] Optimize number of comparisons for heap/heapsort
 implementaion

On Sun, Jan 21, 2024 at 11:36:44PM +0800, Kuan-Wei Chiu wrote:
> Hello,
> 
> The existing implementations of heap/heapsort follow the conventional
> textbook approach, where each heapify operation requires approximately
> 2*log2(n) comparisons. In this series, I introduce a bottom-up variant
> that reduces the number of comparisons during heapify operations to
> approximately log2(n), while maintaining the same number of swap
> operations.
> 
> Thanks,
> Kuan-Wei
> 
> Kuan-Wei Chiu (5):
>   bcachefs: Optimize eytzinger0_sort() using bottom-up heapsort
>   bcachefs: Introduce parent function for sort_cmp_size()
>   bcachefs: Optimize sort_cmp_size() using bottom-up heapsort
>   bcachefs: Optimize number of comparisons in heap_sift_down
>   bcache: Optimize number of comparisons in heap_sift
> 
>  drivers/md/bcache/util.h |  23 +++++----
>  fs/bcachefs/util.c       | 109 ++++++++++++++++++++++++++-------------
>  fs/bcachefs/util.h       |  23 +++++----
>  3 files changed, 98 insertions(+), 57 deletions(-)

Good stuff

While we're looking at this code, we should be doing some cleanup too -
there's no reason for the heap code to be duplicated in bcache and
bcachefs anymore, and it'd also be nice to get fs/bcachefs/eytzinger.h
moved to include/linux and bcache converted to use it.

I also would not be surprised if there's another heap implementation in
include/linux; we'll want to check for that and if there is decide which
is worth keeping.

Would you or Coli be interested in taking that on as well?