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Switch the default global allocator to System, remove alloc_jemalloc, use jemallocator in rustc #36963
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Depends on having stable global allocators.
Since this will result in immediate performance regressions on platforms using jemalloc today we'll need to be sensitive about how the transition is done and make sure it's clear how to regain that allocator perfomance. It might be a good idea to simultaneously publish other allocator crates to demonstrate the value of choice and for benchmark comparisons.
Reacted by Henrique CamposAn alternative I've heard @sfackler advocate from time to time is:
- We make no guarantees about the default allocator, allowing us to choose a fast one like jemalloc
- We expose in stable Rust the ability to request the system allocator as the global allocator
That would allows us to optionally include jemalloc, but if you want the system allocator for heap profiling, valgrind, or other use cases you can choose so.
Reacted by Thiez, Dabo, Daniel P. McGrady and Denys SéguretI would specifically like to jettison jemalloc entirely and use the system allocator. It breaks way too often, it dropped valgrind support, it adds a couple hundred kb to binaries, etc.
Reacted by Sander Maijers, Dabo, Nathan Friedly and Finn BearSome historical speed bumps we've had with jemalloc:
- Currently we don't ship on MSVC or MinGW
- Failed on osx beta releases - rustc(4556,0x7fffcca583c0) malloc: *** malloc_zone_unregister() failed for 0x7fffcca4f548 on OSX 10.12 beta 2 #34674
- Requires a C compiler, makes cross-compiling that much harder. Not only finding the right compiler but passing the right set of options to the C compiler to match what we're doing in Rust.
- Not faster on ARM64 - Jemalloc performance on 64-bit ARM #34476
- Packaging nightmare, distros sometimes want to use their own, but this really doesn't jive well with static linking.
- Valgrind does not work - Valgrind doesn't report allocations with jemalloc on nightly #28224
- Others can rely on jemalloc symbols - Breakage due to changing jemalloc symbol names #31780
- Pulls in a large dep on libc which has glibc versioning issues - Cannot build for mips and armhf with jemalloc #30966
- More problems on MinGW - Upgrade jemalloc, re-enable Windows GNU #31030
- Doesn't work by default on MinGW - Lazy lock may be broken on Windows? jemalloc/jemalloc#310
- Deadlock bugs - Deadlock with mallocx + fork jemalloc/jemalloc#315
- AArch64 + Fedora segfault - Segfault running aarch64-unknown-linux-gnu binaries on Fedora #36994
- OSX deadlock - Deadlock with multithreaded fork on OSX 10.12 jemalloc/jemalloc#895
I'll try to keep this updated as we run into more issues.
Reacted by Stepan Koltsov, Kornel, Dabo, Nathan Friedly, repi, Rett Berg, Colin, hcpl, gurpreetshanky, Eric Shimizu Karbstein and 8 moreReacted by scottmcm and Felipe S. S. Schneiderjemalloc also makes Rust look bad to newcomers, because it makes "Hello World" executables much larger (I know it's not a fair way to judge a language, but people do, and I can't stop myself from caring about size of redistributable executables, too)
Reacted by Sander Maijers, Liigo Zhuang, ShikChen, Mura Li, Arne Keller, Nmlgc, Jesse Wright, hcpl, Dabo, Sergey Bugaev and 9 moreAnother observation - jemalloc seems to add a significant amount of overhead to thread creation, on both Linux and macOS. This hasn't been a major issue for me as we plan to use the system allocator on Fuchsia, but probably something worth looking into.
Reacted by Michael Howell, Rett Berg and phjeltmanOn the glibc side, we would be interested in workloads where jemalloc shows significant benefits. (@djdelorie is working on improving glibc malloc performance.)
- added a commit that references this issue
on Jan 4, 2017 I'd like to see some light benchmarks to get an idea of the magnitude of the default performance regression we can expect.
I'm not sure if this is active, but wanted to voice a recent pain-point:
I am using stable Rust. I wrote a executable. I wrote a dylib. I called one from the other. It explodes because they have different default allocators and I cannot change either on stable.
Independent of which allocator is fasterest, or hardest to maintain, etc., that there is a difference between the default allocators makes the shared library FFI story on stable Rust pretty bad.
Edit: Also, this issue was opened on my birthday so you should just make it happen. <3
Reacted by Josh Bowman-Matthews, Frank McSherry, Jon Gjengset, Alex Kladov, Jonas Schievink, Gabriel Majeri, torpak, Lily and Abhishek KonaReacted by Alex Kladov and Eira FranshamI believe we've also encountered a deadlock on OSX with recent versions of jemalloc - jemalloc/jemalloc#895
33 remaining items
@alexcrichton Is there a tracking issue to track when defaulting to system allocator lands on stable?
rustc 1.31.0 (abe02cefd 2018-12-04)on macOS still links in jemalloc. Thanks!@johnthagen It just has to ride the normal release train. The PR that closed this issue is currently on the beta branch, on track for 1.32.
Reacted by John Hagen@johnthagen We generally close tracking issues when something is done/implemented in the
masterbranch. We don’t track features individually after that, since the release schedule is predictable.In this case, you can see that this issue was closed by #55238 on 2018-11-03, so it likely reached the Nightly channel the next day. Every 6 weeks, Beta becomes Stable and Nightly is forked as the new Beta. So it takes 6 to 12 weeks for a PR merge to reach the Stable channel. https://github.com/rust-lang/rust/blob/master/RELEASES.md shows the dates of past releases and https://forge.rust-lang.org/ the expected date of the next release.
Reacted by John Hagen and Jon GjengsetShould this be tagged with
relnotes?Reacted by Sander Maijers and John HagenGood point! Done.
Reacted by Jon GjengsetI am quite saddened by this. PL-scale memory throughout regressions like this will use a lot more energy, cost most users (who are unlikely to learn about GlobalAlloc) more on their server bills, and blunt the surprising bliss experienced by so many newcomers whose uncertain first steps blow their previous implementations out of the water.
Binary size is a vanity metric for computing at scale, and for those who require it to be smaller, they have the flexibility to change.
This has real ethical implications, as our DCs are set to consume 20% of the world's electricity by 2025, and the decisions made by those shaping the foundational layers have massive implications.
Overriding GlobalAlloc is not a realistic option for authors of allocation intensive libraries, as it prevents users from using tools like the llvm sanitizers etc...
As engineers building foundational infrastructure, we have an ethical obligation to the planet to minimize the costs we impose on it. This decision was made in direct contradiction of this responsibility to our shared home. Amazing efficiency by default on the platform that is the main driver of world-wide datacenter power consumption is a precious metric for a language with as bright a future for massive scale adoption as rust.
Reacted by Mateusz Mikuła, Jon Gjengset, tesuji, Shirshak, Cliff Hammerschmidt and John Boehr@spacejam I don't think it's quite fair to characterize this as that grand of a problem. It's not as though jemalloc exclusively makes things faster, and thus not as though this is universally a regression. Quite to the contrary. There are some workloads that are made much better by this. This change also means that, as system allocators improve, so will that of Rust programs. This would not be the case for a compiled-in memory allocator. If you want to go down the life-cycle analysis path, I think it could also be argued that we are saving countless person hours by allowing the user of standardized tools from people who previously had to waste time trying to figure out why valgrind or what didn't just work. Along those same lines, one could argue that every change to the standard library has wide-reaching implications on global energy use, but a) that impact is minute; b) that impact is basically impossible to predict; and c) it is infeasible to perform that kind of analysis on any kind of representative scale for every (if any) change.
Reacted by Andrew Gallant, Mateusz Mikuła, Sander Maijers, Stephan Sokolow, Gibson Fahnestock, Shuni, Shirshak, Pâris DOUADY, danielocfb and 1 more
Updated description
A long time coming, this issue is that we should implement these changes simultaneously:
alloc_jemalloccratestd::alloc::System. While currently the default for cdylib/staticlib, it's not the default for staticlib/executablejemallocatorcrate to rustc, but only rustcalloc_systemcrateWe for the longest time have defaulted to jemalloc as the default allocator for Rust programs. This has been in place since pre-1.0 and the vision was that we'd give programs a by-default faster allocator than what's on the system. Over time, this has not fared well:
#[global_allocator]to opt-in to a jemalloc-based global allocator (through thejemallocatoror any other allocator crate).The compiler, however still receives a good deal of benefit from using jemalloc (measured in #55202 (comment)). If that link is broken, it's basically a blanket across-the-board 8-10% regression in compile time for many benchmarks. (apparently the max rss also regressed on many benchmarks!). For this reason, we don't want to remove jemalloc from rustc itself.
The rest of this issue is now going to be technical details about how we can probably get rid of
alloc_jemallocwhile preserving jemalloc in rustc itself. The tier 1 platforms that usealloc_jemallocwhich this issue will be focused on are:Jemalloc is notably disabled on all Windows platforms (I believe due to our inability to ever get it building over there). Furthermore Jemalloc is enabled on some linux platforms but I think ended up basically being disabled on all but the above. This I believe narrows the targets we need to design for, as we basically need to keep the above working.
Note that we also have two modes of using jemalloc. In one mode we could actually use jemalloc-specific API functions, like
alloc_jemallocdoes today. We could also use the standard API it has and the support to hook into the standard allocator on these two platforms. It's not been measured (AFAIK) at this time the tradeoff between these two strategies. Note that in any case we want to route LLVM's allocations to jemalloc, so we want to be sure to hook into the default allocator somehow.I believe that this default allocator hooking on Linux works by basically relying on its own symbol
mallocoverriding that inlibc, routing all memory allocation to jemalloc. I'm personally quite fuzzy on the details for OSX, but I think it has something to do with "zone allocators" and not much to do with symbol names. I think this means we can build jemalloc without symbol prefixes on Linux, and with symbol prefixes on OSX, and we should be able to, using that build, override the default allocator in both situations.I would propose, first, a "hopefully easy" route to solve this:
jemalloc_sys, pulling in all of jemalloc itself. This should, with the right build configuration, mean that we're not using jemalloc everywhere in the compiler (just as we're rerouting LLVM we're rerouting the compiler).I'm testing out the performance of this in #55217 and will report back with results. Results are that this is universally positive almost! @alexcrichton will make a PR.
Failing this @alexcrichton has ideas for a more invasive solution to use jemalloc-specific API calls in rustc itself, but hopefull that won't be necessary...
Original Description
@alexcrichton and I have increasingly come to think that Rust should not maintain jemalloc bindings in tree and link it by default. The primary reasons being:
For the sake of consistency and maintenance we'd prefer to just always use the system allocator, and make jemalloc an easy option to enable via the global allocator and a jemalloc crate on crates.io.