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On Sun, Oct 27, 2019 at 09:59, Florian Weimer <fw@deneb.enyo.de> wrote:
* Mark Wielaard:Current glibc versions have a thread-local fast path, which should address some of these concerns. It's still not a bump-pointer allocator, but at least there are no atomics on that path.Since which version of glibc is there a thread-local fast path?It was added in: commit d5c3fafc4307c9b7a4c7d5cb381fcdbfad340bcc Author: DJ Delorie <dj@delorie.com <mailto:dj@delorie.com>> Date: Thu Jul 6 13:37:30 2017 -0400 Add per-thread cache to malloc So glibc 2.26. But it is a build-time option, enabled by default, but it can be switched off by distributions.
I doubt any non-mobile distros would disable it, the cost seems fairly small.
My main concern is that it seems like chunks will only enter the thread-local cache in the presence of free()s (since they have to enter the "smallbins" or "fastbins" first, and those two at a glance seem to be filled very lazily or on free()); since the free()s are all on dwarf_end this would pose an issue. I could also be entirely mistaken, glibc is by no means a simple piece of code.
According to the comments, there might also be a 16 byte overhead per allocation, which would explode the small allocations considerably.
-Jonathon
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