On Sun, Jan 21, 2024 at 12:41:55PM -0500, Kent Overstreet wrote: > On Mon, Jan 22, 2024 at 12:55:51AM +0800, Kuan-Wei Chiu wrote: > > 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. > > So that has the advantage of more readable code - functions instead of > macros - whereas my version has the type safe interface. > > We could combine the two approaches, and put a type-safe interface on > top of the min_heap.h code with some small macro wrappers - see > generic-radix-tree.h for an example of how that's done. Without modifying the interface provided by min_heap.h, it seems challenging to implement the functionality of heap_add due to the relationship with heap_setbackpointer. Additionally, when looking into the code in generic-radix-tree.h, should we replace type[0] with type[]? This is because zero-length arrays are deprecated language features mentioned in document [1]. Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays [1] > > min_heap.h has only one user though? I don't think I can quite believe > that's the only other code in the kernel using a heap, there must be > more open coded out there... I'm not sure why, but it seems that in the kernel, other places using the heap implement their own subsystem-specific solutions rather than utilizing a generic heap interface. For instance, kernel/sched/cpudeadline.c and net/sched/sch_cake.c both have their own implementations.
