linux-kernel - Re: [PATCH v2 04/15] lib min_heap: Add type safe interface

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Message-ID: <mi3uq4gqvseubfiylslxfrnwupfzopz753md5f53v6brlgiamv@l5bxmctqnz6g>
Date: Thu, 21 Mar 2024 17:22:14 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Kuan-Wei Chiu <visitorckw@...il.com>
Cc: colyli@...e.de, msakai@...hat.com, peterz@...radead.org, 
	mingo@...hat.com, acme@...nel.org, namhyung@...nel.org, akpm@...ux-foundation.org, 
	bfoster@...hat.com, mark.rutland@....com, alexander.shishkin@...ux.intel.com, 
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com, 
	jserv@...s.ncku.edu.tw, dm-devel@...ts.linux.dev, linux-bcache@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 04/15] lib min_heap: Add type safe interface

On Thu, Mar 21, 2024 at 07:57:47PM +0800, Kuan-Wei Chiu wrote:
> On Wed, Mar 20, 2024 at 04:56:57PM -0400, Kent Overstreet wrote:
> > On Wed, Mar 20, 2024 at 10:54:06PM +0800, Kuan-Wei Chiu wrote:
> > > Introduce a type-safe interface for min_heap by adding small macro
> > > wrappers around functions and using a 0-size array to store type
> > > information. This enables the use of __minheap_cast and
> > > __minheap_obj_size macros for type casting and obtaining element size.
> > > The implementation draws inspiration from generic-radix-tree.h,
> > > eliminating the need to pass element size in min_heap_callbacks.
> > 
> > let's avoid the heap->heap.nr - darray (fs/bcachefs/darray.h) has a
> > trick for that. All heaps have the same memory layout, so we can just
> > cast to a void pointer heap to get something the C code can use.
> >
> If I understand correctly, you're suggesting adding APIs similar to
> darray_top(), darray_first(), and darray_last() within min_heap and
> having them return a pointer. However, some users are using heap.nr in
> conditional statements instead of utilizing heap.nr for memory
> operations, so returning pointers may not be as convenient. What about
> adding get and set functions for nr instead?

No, I mean not having separate inner and outer types. Want me to sketch
something out?