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

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Date: Mon, 22 Jan 2024 00:55:51 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
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 11:21:06AM -0500, Kent Overstreet wrote:
> 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.
>
Yes, we have 'min_heap.h' in include/linux.

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