Date: Wed, 21 Sep 2022 02:35:17 +0800 From: baiyang <baiyang@...il.com> To: musl <musl@...ts.openwall.com> Cc: "Quentin Rameau" <quinq@...th.space>, "Florian Weimer" <fweimer@...hat.com> Subject: Re: Re: The heap memory performance (malloc/free/realloc) is significantly degraded in musl 1.2 (compared to 1.1) > So what you're actually trying to do is more clear now. > And this is something that you should do on the “application layer”, > not expect the libc to magically taking care of this. Yes, we just do this at the application layer with the help of APIs such as malloc_usable_size. You can look at the previous emails, isn't that what we're discussing? > They want to know if realloc will resize the allocation in-place so > the internal memcpy will not happen. > AIUI, what they really need is not "usable_size", but "cost estimation > for resizing allocation at pointer P to size S". Which I believe they > try to deduce from malloc_usable_size. Yes, from malloc_usable_size, the size that the application layer actually needs to copy, and other parameters like the OS, allocator, etc. -- Best Regards BaiYang baiyang@...il.com http://i.baiy.cn **** < END OF EMAIL > **** From: Alexander Monakov Date: 2022-09-21 02:26 To: musl CC: Quentin Rameau; Florian Weimer Subject: 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 so the internal memcpy will not happen. AIUI, what they really need is not "usable_size", but "cost estimation for resizing allocation at pointer P to size S". Which I believe they try to deduce from malloc_usable_size. Alexander Content of type "text/html" skipped
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