On Mon, Jan 22, 2024 at 11:06:54PM +0800, Kuan-Wei Chiu wrote: > 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. min_heap.h has the same functionality, different interface - updating the callers for an interface change is fine. > > 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]. Zero length arrays are deprecated as VLAs, but this isn't a VLA - we're not storing anything there, the variable is just so that macros have access to the type. > 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. Sounds like a fun cleanup project :)
