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From: Alexander MonakovDate: 2022-09-21 02:26To: muslSubject: Re: [musl] The heap memory performance (malloc/free/realloc) is significantly degraded in musl 1.2 (compared to 1.1)On Tue, 20 Sep 2022, Rich Felker wrote:> Exactly. This can be done entirely at the application layer just by> keeping track of the size you allocated. In the above example, the> number 256 kB is a red herring. Yes the> "malloc(300KB)+memcpy(256KB)+free(256KB)" is wasteful, but the> "malloc(300KB)+memcpy(200KB)+free(200KB)" would be comparably wasteful> when you only want to preserve the first 2K, and you can make the> decision that it would be wasteful, and that you instead just want to> allocate a new buffer yourself and memcpy 2K, just by knowing the> original 200KB, without any knowledge of malloc_usable_size.They want to know if realloc will resize the allocation in-place sothe internal memcpy will not happen.AIUI, what they really need is not "usable_size", but "cost estimationfor resizing allocation at pointer P to size S". Which I believe theytry to deduce from malloc_usable_size.Alexander