> We plan to deliver improvements to [..] purging mechanisms<p>During my time at Facebook, I maintained a bunch of kernel patches to improve jemalloc purging mechanisms. It wasn't popular in the kernel or the security community, but it was more efficient on benchmarks for sure.<p>Many programs run multiple threads, allocate in one and free in the other. Jemalloc's primary mechanism used to be: madvise the page back to the kernel and then have it allocate it in another thread's pool.<p>One problem: this involves zero'ing memory, which has an impact on cache locality and over all app performance. It's completely unnecessary if the page is being recirculated within the same security domain.<p>The problem was getting everyone to agree on what that security domain is, even if the mechanism was opt-in.<p><a href="https://marc.info/?l=linux-kernel&m=132691299630179&w=2" rel="nofollow">https://marc.info/?l=linux-kernel&m=132691299630179&w=2</a>
I'm really surprised to see you still hocking this.<p>We did extensive benchmarking of HHVM with and without your patches, and they were proven to make no statistically significant difference in high level metrics. So we dropped them out of the kernel, and they never went back in.<p>I don't doubt for a second you can come up with specific counterexamples and microbenchnarks which show benefit. But you were unable to show an advantage at the system level when challenged on it, and <i>that's</i> what matters.
You probably weren't there when servers were running for many days at a time.<p>By the time you joined and benchmarked these systems, the continuous rolling deployment had taken over. If you're restarting the server every few hours, of course the memory fragmentation isn't much of an issue.<p>> But you were unable to show an advantage at the system level when challenged on it, and that's what matters.<p>You mean 5 years after I stopped working on the kernel and the underlying system had changed?<p>I don't recall ever talking to you on the matter.
> By the time you joined and benchmarked these systems, the continuous rolling deployment had taken over<p>Nope, I started in 2014.<p>> I don't recall ever talking to you on the matter.<p>I recall. You refused to believe the benchmark results and made me repeat the test, then stopped replying after I did :)
The patches were written in 2011 and published in 2012. They did what they were supposed to at the time.<p>For the peanut gallery: this is a manifestation of an internal eng culture at fb that I wasn't particularly fond of. Celebrating that "I killed X" and partying about it.<p>You didn't reply to the main point: did you benchmark a server that was running several days at a time? Reasonable people can disagree about whether this a good deployment strategy or not. I tend to believe that there are many places which want to deploy servers and run for months if not days.
This is why I love hacker news. I learn so much from these moments.
Like "never work at Meta unless you can out-toxic your coworkers".
Yea I knew meta was toxic, but publicly beefing over something over a decade ago is a whole other matter. I can’t even remember what I was working on 10 years ago, and even if I did I wouldn’t be bringing people down that much later.
The problem is a lot of very strong engineers are also very difficult to work with. I worked at Meta too and can tell you the other side of the coin is that people who were too toxic could get canned as well!
Yes, I have worked with the strong but arrogant/snarky engineers. Luckily most of them got canned or forced out because the environment they create around themselves more than negates the positive impact they have. The strongest engineers I have worked with are all humble and kind.<p>It is their loss, I cannot imagine letting a minor work quarrel live rent free in my head for over a decade. I feel bad enough when something is stuck in my mind for a week.
Yeah, I am loving the <i>public</i> mudslinging over shit from 10 years ago, like high school girls fighting. This is like the FAANG version of the TV show Suits. We can call it FAANGs and use Midjorney to create the cover art and give the actors vampire fangs.<p>On a more serious note, it seems like any hyper competitive company eventually spirals into an awful, toxic working env.
Funny, I was thinking what a relief it was to see people making their arguments frankly like on the HN of 10+ years ago.
Inside Meta, engineers are one of the kindest group of people.<p>This thread would've been way more fun with a couple of middle managers and product managers in the mix ;-)
Like "Hey, I wonder if Conway's Law works both ways. Huh. Wow. It looks like that is indeed the case."
I came here for the article, stayed for the drama.
I wouldn't be surprised if both 'adsharma' and 'jcalvinowens' were right, just at different points in time, perhaps in a bit different context. Things change.
Maybe I'm misreading, but considering it OK to leak memory contents across a process boundary because it's within a cgroup sounds wild.
It wasn't any cgroup. If you put two untrusting processes in a memory cgroup, there is a lot that can go wrong.<p>If you don't like the idea of memory cgroups as a security domain, you could tighten it to be a process. But kernel developers have been opposed to tracking pages on a per address space basis for a long time. On the other hand memory cgroup tracking happens by construction.
> across a process boundary<p>> within a cgroup<p>Note the complementary language usage here. You seem to have interpreted that as me writing that it didn't matter what cgroup they are in, which is an odd thing to claim that I implied. I meant <i>within the same</i> cgroup obviously.<p>Yes, you can read memory out of another process through other means.. but you shouldn't map pages, be able to read them and see what happened in another process. That's the wild part. It strikes me as asking for problems.<p>I was unaware of MAP_UNINITIALIZED, support for which was disabled by default and for good reason. Seems like it was since removed.
What metrics were improved by your patches?
I recently started using Microsoft's mimalloc (via an LD_PRELOAD) to better use huge (1 GB) pages in a memory intensive program. The performance gains are significant (around 20%). It feels rather strange using an open source MS library for performance on my Linux system.<p>There needs to be more competition in the malloc space. Between various huge page sizes and transparent huge pages, there are a lot of gains to be had over what you get from a default GNU libc.
We evaluated a few allocators for some of our Linux apps and found (modern) tcmalloc to consistently win in time and space. Our applications are primarily written in Rust and the allocators were linked in statically (except for glibc). Unfortunately I didn't capture much context on the allocation patterns. I think in general the apps allocate and deallocate at a higher rate than most Rust apps (or more than I'd like at least).<p>Our results from July 2025:<p>rows are <allocator>: <RSS>, <time spent for allocator operations><p><pre><code> app1:
glibc: 215,580 KB, 133 ms
mimalloc 2.1.7: 144,092 KB, 91 ms
mimalloc 2.2.4: 173,240 KB, 280 ms
tcmalloc: 138,496 KB, 96 ms
jemalloc: 147,408 KB, 92 ms
app2, bench1
glibc: 1,165,000 KB, 1.4 s
mimalloc 2.1.7: 1,072,000 KB, 5.1 s
mimalloc 2.2.4:
tcmalloc: 1,023,000 KB, 530 ms
app2, bench2
glibc: 1,190,224 KB, 1.5 s
mimalloc 2.1.7: 1,128,328 KB, 5.3 s
mimalloc 2.2.4: 1,657,600 KB, 3.7 s
tcmalloc: 1,045,968 KB, 640 ms
jemalloc: 1,210,000 KB, 1.1 s
app3
glibc: 284,616 KB, 440 ms
mimalloc 2.1.7: 246,216 KB, 250 ms
mimalloc 2.2.4: 325,184 KB, 290 ms
tcmalloc: 178,688 KB, 200 ms
jemalloc: 264,688 KB, 230 ms
</code></pre>
tcmalloc was from github.com/google/tcmalloc/tree/24b3f29.<p>i don't recall which jemalloc was tested.
I’m surprised (unless they replaced the core tcmalloc algorithm but kept the name).<p>tcmalloc (thread caching malloc) assumes memory allocations have good thread locality. This is often a double win (less false sharing of cache lines, and most allocations hit thread-local data structures in the allocator).<p>Multithreaded async systems destroy that locality, so it constantly has to run through the exception case: A allocated a buffer, went async, the request wakes up on thread B, which frees the buffer, and has to synchronize with A to give it back.<p>Are you using async rust, or sync rust?
modern tcmalloc uses per CPU caches via rseq [0]. We use async rust with multithreaded tokio executors (sometimes multiple in the same application). so relatively high thread counts.<p>[0]: <a href="https://github.com/google/tcmalloc/blob/master/docs/design.md" rel="nofollow">https://github.com/google/tcmalloc/blob/master/docs/design.m...</a>
also:<p>1. tcmalloc is actually the only allocator I tested which was not using thread local caches. even glibc malloc has tcache.<p>2. async executors typically shouldn’t have tasks jumping willy nilly between threads. i see the issue u describe more often with the use of thread pools (like rayon or tokio’s spawn_blocking). i’d argue that the use of thread pools isn’t necessarily an inherent feature of async executors. certainly tokio relies on its threadpool for fs operations, but io-uring (for example) makes that mostly unnecessary.
> I’m surprised (unless they replaced the core tcmalloc algorithm but kept the name).<p>Indeed, it's not the old gperftools version.<p>Blog: <a href="https://abseil.io/blog/20200212-tcmalloc" rel="nofollow">https://abseil.io/blog/20200212-tcmalloc</a><p>History / Diffs: <a href="https://google.github.io/tcmalloc/gperftools.html" rel="nofollow">https://google.github.io/tcmalloc/gperftools.html</a>
That’s a considerable regression for mimalloc between 2.1 and 2.2 – did you track it down or report it upstream?<p>Edit: I see mimalloc v3 is out – I missed that! That probably moots this discussion altogether.
This is similar to what I experienced when I tested mimalloc many years ago. If it was faster, it wasn't faster by much, and had pretty bad worst cases.
If you go into Dr Dobbs, The C/C++ User's Journal and BYTE digital archives, there will be ads of companies whose product was basically special cased memory allocator.<p>Even toolchains like Turbo Pascal for MS-DOS, had an API to customise the memory allocator.<p>The one size fits all was never a solution.
One of the best parts about GC languages is they tend to have much more efficient allocation/freeing because the cost is much more lumped together so it shows up better in a profile.
Agreed, however there is also a reason why the best ones also pack multiple GC algorithms, like in Java and .NET, because one approach doesn't fit all workloads.
When it works. Many programs in GC language end up fighting the GC by allocating a large buffer and managing it by hand anyway because when performance counts you can't have allocation time in there at all. (you see this in C all the time as well)
That's generally a bad idea. Not always, but generally.<p>It was a better idea when Java had the old mark and sweep collector. However, with the generational collectors (which are all Java collectors now. except for epsilon) it's more problematic. Reusing buffers and objects in those buffers will pretty much guarantees that buffer ends up in oldgen. That means to clear it out, the VM has to do more expensive collections.<p>The actual allocation time for most of Java's collectors is almost 0, it's a capacity check and a pointer bump in most circumstances. Giving the JVM more memory will generally solve issues with memory pressure and GC times. That's (generally) a better solution to performance problems vs doing the large buffer.<p>Now, that said, there certainly have been times where allocation pressure is a major problem and removing the allocation is the solution. In particular, I've found boxing to often be a major cause of performance problems.
If your workload is very regular, you can still do better with an arena allocator. Within the arena, it uses the same pointer-bump allocation as Java normally uses, but then you can free the whole area back to the start by resetting the pointer to its initial value. If you use the arena for servicing a single request, for instance, you then reset as soon as you're done with the request, setting you up with a totally free area for the next request. That's more efficient than a GC. But it also requires your algorithm to fall into that pattern where you KNOW that you can and should throw everything from the request away. If you can't guarantee that, then modern collectors are pretty magical and tunable.
If people didn't need to do it, they wouldn't generally do it. Not always, but generally.
People do stuff they shouldn't all the time.<p>For example, some code I had to clean up pretty early on in my career was a dev, for unknown reasons, reinventing the `ArrayList` and then using that invention as a set (doing deduplication by iterating over the elements and checking for duplicates). It was done in the name of performance, but it was never a slow part of the code. I replaced the whole thing with a `HashSet` and saved ~300 loc as a result.<p>This individual did that sort of stuff all over the code base.
Reinventing data structures poorly is very common.<p>Heap allocation in java is something trivial happens constantly. People typically do funky stuff with memory allocation because they have to, because the GC is causing pauses.<p>People avoid system allocators in C++ too, they just don't have to do it because of uncontrollable pauses.
> People typically do funky stuff with memory allocation because they have to<p>This same dev did things like putting what he deemed as being large objects (icons) into weak references to save memory. When the references were collected, invariably they had to be reloaded.<p>That was not the source of memory pressure issues in the app.<p>I've developed a mistrust for a lot of devs "doing it because we have to" when it comes to performance tweaks. It's not a never thing that a buffer is the right thing to do, but it's not been something I had to reach for to solve GC pressure issues. Often times, far more simple solutions like pulling an allocation out of the middle of a loop, or switching from boxed types to primatives, was all that was needed to relieve memory pressure.<p>The closest I've come to it is replacing code which would do an expensive and allocation heavy calculation with a field that caches the result of that calculation on the first call.
Premature optimization is the root of all evil.
I'm not sure why you're rationale for how to deal with garbage collected memory is based on a guy that didn't know standard data structures and your own gut feelings.<p>Any program that cares about performance is going to focus on minimizing memory allocation first. The difference between a GCed language like java is that the problems manifest as gc pauses that may or may not be predictable. In a language like C++ you can skip the pauses and worry about the overall throughput.
Any extra throughput is far overshadowed by trying to control pauses and too much heap allocations happening because too much gets put on the heap. For anything interactive the options are usually fighting the gc or avoiding gc.
I remember in the early days of web services, using the apache portable runtime, specifically memory pools.<p>If you got a web request, you could allocate a memory pool for it, then you would do all your memory allocations from that pool. And when your web request ended - either cleanly or with a hundred different kinds of errors, you could just free the entire pool.<p>it was nice and made an impression on me.<p>I think the lowly malloc probably has lots of interesting ways of growing and changing.
This is called “an arena” more generally, and it is in wide use across many forms of servers, compilers, and others.
Look into talloc, used inside Samba (and other FLOSS projects like sssd). Exactly this.
In many cases you can also do better than using malloc e.g. if you know you need a huge page, map a huge page directly with mmap<p>Yes, if you want to use huge pages with arbitrary alloc/free, then use a third-party malloc. If your alloc/free patterns are not arbitrary, you can do even better. We treat malloc as a magic black box but it's actually not very good.
I think some operating system improvements could get people motivated to use huge pages a lot better. In particular make them less fragile on linux and make them not need admin rights on windows. The biggest factor causing problems there is that neither OS can swap a 2MB page. So someone needs to care enough to fix that.
I used mimalloc to run zenlisp under OpenBSD as it would clash with the paranoid malloc of base.
I feel like the real thing that needs to change is we need a more expressive allocation interface than just malloc/realloc. I'm sure that memory allocators could do a significantly better job if they had more information about what the program was intending to do.
There are, look no further than jemalloc API surface itself:<p><a href="https://jemalloc.net/jemalloc.3.html" rel="nofollow">https://jemalloc.net/jemalloc.3.html</a><p>One thing to call out: sdallocx integrates well with C++'s sized delete semantics: <a href="https://isocpp.org/files/papers/n3778.html" rel="nofollow">https://isocpp.org/files/papers/n3778.html</a>
Just out of curiosity are you getting 1GB huge pages on Xeon or some other platform? I always thought this class of page is the hardest to exploit, considering that the machine only has, if I recall correctly, one TLB slot for those.
Modern x86_64 has supported multiple page sizes for a long time. I'm on commodity Zen 5 hardware (9900X) with 128 GiB of RAM. Linux will still use a base page size of 4kb but also supports both 2 MiB and 1 GiB huge pages. You can pass something like `default_hugepagesz=2M hugepagesz=1G hugepages=16` to your kernel on boot to use 2 MiB pages but reserve 16 1 GiB pages for later use.<p>The nice thing about mimalloc is that there are a ton of configurable knobs available via env vars. I'm able to hand those 16 1 GiB pages to the program at launch via `MIMALLOC_RESERVE_HUGE_OS_PAGES=16`.<p>EDIT: after re-reading your comment a few times, I apologize if you already knew this (which it sounds like you did).
<p><pre><code> > commodity
> zen 5
> 128GiB
</code></pre>
Are you from the future?
Right but on Intel the 1G page size has historically been the odd one. For example Skylake-X has 1536 L2 shared TLB entries for either 4K or 2M pages, but it only has 16 entries that can be used for 1G pages. It wasn't unified until Cascade Lake. But Skylake-like Xeon is still incredibly common in the cloud so it's hard to target the later ones.
So for any process that's using less than 16GB, it's a significant performance boost. And most processes using more RAM, but not splitting accesses across more than 16 zones in rapid succession, will also see a performance boost.<p>My old Intel CPU only has 4 slots for 1GB pages, and that was enough to get me about a 20% performance boost on Factorio. (I think a couple percent might have been allocator change but the boost from forcing huge pages was very significant)
If there is so much performance difference among generic allocators, it means you need semantic optimized allocators (unless performance is actually not that much important in the end).
You are not wrong and this is indeed what zig is trying to push by making all std functions that allocate take a allocator parameter.
Agreed mostly. Going from standard library to something like jemalloc or tcmalloc will give you around 5-10% wins which can be significant, but the difference between those generic allocators seem small. I just made a slab allocator recently for a custom data type and got speedups of 100% over malloc.
[dead]
I've been using jemalloc for over 10 years and don't really see a need for it to be updated. It always holds up in benchmarks against any new flavor of the month malloc that comes out.<p>Last time I checked mimalloc which was admittedly a while ago, probably 5 years, it was noticebly worse and I saw a lot of people on their github issues agreeing with me so I just never looked at it again.
Mimalloc v3 has just come out (about a month ago) and is a significant improvement over both v2 and v1 (what you likely last tested)
Benchmarks age fast. Treating a ten-year-old allocator as done just because it still wins old tests is tempting fate, since distros, glibc, kernel VM behavior, and high-core alloc patterns keep moving and the failures usually show up as weird regressions in production, not as a clean loss on someone's benchmark chart.
Related. Others?<p><i>Jemalloc Postmortem</i> - <a href="https://news.ycombinator.com/item?id=44264958">https://news.ycombinator.com/item?id=44264958</a> - June 2025 (233 comments)<p><i>Jemalloc Repositories Are Archived</i> - <a href="https://news.ycombinator.com/item?id=44161128">https://news.ycombinator.com/item?id=44161128</a> - June 2025 (7 comments)
One has to wonder if this due to the global memory shortage. ("Oh - changing our memory allocator to be more efficient will yield $XXM dollar savings over the next year").
Facebook had talks already years ago (10+) - nobody was allowed to share real numbers, but several facebook employed where allowed to share that the company has measured savings from optimizations. Reading between the lines, a 0.1% efficiency improvement to some parts of Facebook would save them $100,000 a month (again real numbers were never publicly shared so there is a range - it can't be less than $20,000), and so they had teams of people whose job it was to find those improvements.<p>Most of the savings seemed to come from HVAC costs, followed by buying less computers and in turn less data centers. I'm sure these days saving memory is also a big deal but it doesn't seem to have been then.<p>The above was already the case 10 years ago, so LLMs are at most another factor added on.
I don't have many regrets about having spent my career in (relatively) tiny companies by comparison, but it sure does sound fun to be on the other side for this kind of thing - the scale where micro-optimizations have macro impact.<p>In startups I've put more effort into squeezing blood from a stone for far less change; even if the change was proportionally more significant to the business. Sometimes it would be neat to say "something I did saved $X million dollars or saved Y kWh of energy" or whatever.
I've worked on optimizing systems in that ballpark range, memory is worth saving but it isn't necessarily 1:1 with increasing revenue like CPU is. For CPU we have tables to calculate the infra cost savings (we're not really going to free up the server, more like the system is self balancing so it can run harder with the freed CPU), but for memory as long as we can load in whatever we want to (rec systems or ai models) we're in the clear so the marginal headroom isn't as important. It's more of a side thing that people optimizing CPU also get wins in by chance because the skillsets are similar.
I've heard of some people getting banned from FB to save memory space? Surely that can't be the case but I swear I've seen something like that
> LLMs are at most another factor added on<p>At most...
Think 10x rather than 0.1x or 1x.
On top of cost, they probably cannot get as much memory as they order in a timely fashion so offsetting that with greater efficiency matters right now.
Yeah, identifying single-digit millions of savings out of profiles is relatively common practice at Meta. It's ~easy to come up with a big number when the impact is scaled across a very large numbers of servers. There is a culture of measuring and documenting these quantified wins.
With the reputation of that company, one can wonder a lot of backstories that are even more depressing than a memory shortage.
Not just shortage, any improvements to LLMs/electricity/servers memory footprint is becoming much more valuable as the time goes. If we can get 10% faster, you can easily get a lead in the LLM race. The incentives to transparently improving performance are tremendous
Oooh maybe finally time for lovingly hand-optimized assembly to come back in fashion! (It probably has in AI workloads or so I daydream)
> changing our memory allocator<p>they've been using jemalloc (and employing "je") since 2009.
As an Australian who was just made redundant from a role that involved this type of low level programming - I love working on these these kinds of challenges.<p>I'm saddened that the job market in Australia is largely React CRUD applications and that it's unlikely I will find a role that lets me leverage my niche skill set (which is also my hobby)
I know this isn’t who’s hiring thread, but we are hiring in AU for low-level data processing and have interesting performance challenges.<p>Link in bio.
Speaking as an Australian that works on React CRUD applications because there's nothing else in the market, I've been reading through this thread thinking the exact same thing.
Google had some position open working on the kernel for ChromeOS, and Microsoft had some positions working on data center network drivers.<p>I applied for both and got ghosted, haha.<p>I also saw a government role as a security researcher. Involves reverse engineering, ghidra and that sort of thing. Super awesome - but the pay is extremely uncompetitive. Such a shame.<p>Other than that, the most interesting roles are in finance (like HFT) - where you need to juggle memory allocations, threads and use C++ (hoping I can pitch Rust but unlikely).<p>Sadly they have a reputation of having pretty rough cultures, uncompetitive salaries and it's all in-office
I hear you. Actually I read this thread because we’re using jemalloc in an embedded product. The only way I found to work on interesting problems here was to work for myself. (Having said that I think Apple might have some security research in Canberra? Years ago there was LinuxCare there and a lot of smart people. But that was in 2003…)
Some of this remote stuff might interest you:<p><a href="https://www.igalia.com/jobs/open/" rel="nofollow">https://www.igalia.com/jobs/open/</a>
Not sure if it's the domain you're interested in, but there are quite a few HFT firms with offices in Australia.<p>The one I know of (IMC trading) does a lot of low level stuff like this and is currently hiring.
I'm actually looking at HFT companies. Hoping I find one that allows remote working - but looks like there are basically no remote roles going at the moment
I just tried to apply for IMC, the form on their careers page is broken. Looks like that's the first boss to defeat, haha
SIG is hiring for some roles in Sydney: <a href="https://careers.sig.com/global-experienced" rel="nofollow">https://careers.sig.com/global-experienced</a>
I have a relative in Australia who was hired by some type of consultancy to work on Samba, but I don't know what work he was doing.
> With the leverage jemalloc provides however, it can be tempting to realize some short-term benefit. It requires strong self-discipline as an organization to resist that temptation and adhere to the core engineering principles.<p>This doesn't quite read properly to me. What does it actually mean, does anyone know?
Opening up strong with a gigantic merge of the stuff they've been working on in their own fork: <a href="https://github.com/jemalloc/jemalloc/pull/2863" rel="nofollow">https://github.com/jemalloc/jemalloc/pull/2863</a>
I remember I was a senior lead softeng of a worldbank funded startup project, and have deployed Ruby with jemalloc in prod. There's a huge noticeable speed and memory efficiency. It did saved us a lot of AWS costs, compare to just using normal Ruby. This was 8 years ago, why haven't projects adopt it yet as de facto.
Usually lack of knowledge that such a thing exists, or just plain ol' momentum. Changing something long in production at established companies, even if there is a tangible benefit, can be a real challenge.
Is there a concise timelime/history of this? I thought jemalloc was 100% open source, why is Meta in control of it?
Jason Evans (the creator of jemalloc) recounted the entire thing last year: <a href="https://jasone.github.io/2025/06/12/jemalloc-postmortem/" rel="nofollow">https://jasone.github.io/2025/06/12/jemalloc-postmortem/</a>
"Were I to reengage, the first step would be at least hundreds of hours of refactoring to pay off accrued technical debt."<p>Facebook's coding AIs to the rescue, maybe? I wonder how good all these "agentic" AIs are at dreaded refactoring jobs like these.
Refactor doesn't mean just artificial puff-up jobs, it's very likely internal changes and reorganization (hence 100s of hours).<p>There are not many engineers capable of working on memory allocators, so adding more burden by agentic stuff is unlikely to produce anything of value.
> Facebook's coding AIs to the rescue, maybe? I wonder how good all these "agentic" AIs are at dreaded refactoring jobs like these.<p>No.<p>This is something you shouldn't allow coding agents anywhere near, unless you have expert-level understanding required to maintain the project like the previous authors have done without an AI for years.
Hm, I wonder.<p>I've done some work in this sort of area before, though not literally on a malloc. Yes you very much want to be careful, but ultimately it's the tests that give you confidence. Pound the heck out of it in multithreaded contexts and test for consistency.
AI is more than happy to declare the test wrong and “fix it” if you’re not careful. And the cherry on top is that sometimes the test could be wrong or need updating due to changed behavior. So…
> ...but ultimately it's the tests that give you confidence. Pound the heck out of it in multithreaded contexts and test for consistency.<p>I don't think so.<p>Even on LLM generated code, it is still not enough and you cannot trust it. They can pass the tests and still cause a regression and the code will look seemingly correct, for example in this case study [0].<p>[0] <a href="https://sketch.dev/blog/our-first-outage-from-llm-written-code" rel="nofollow">https://sketch.dev/blog/our-first-outage-from-llm-written-co...</a>
If you filter the commits to the past five years, four of the top six committers are Meta employees. The other two might be as well, it just doesn't say that on their Github / personal website.
We migrated to jemalloc from glibc malloc two years ago and saw 15-20% memory reduction in our Python services. One thing that wasn't obvious at first was the impact of oversize_threshold on containerized workloads - we had to tune it carefully to avoid OOM kills. Has anyone benchmarked jemalloc vs mimalloc for long-running services?
jemalloc 5.2.1 vs mimalloc v3.2.8 in Rust software processing hundreds of Terabytes. Could not measure a meaningful difference, but mimalloc would release freed memory to the OS a lot sooner and therefore look nicer in top. That said, older mimalloc from default rust crate would cause memory corruption with large allocations >2Gb in about 5% of the cases. Stuck with battle hardened jemalloc for now.
Mimalloc my beloved. The fact that jemalloc is this fiendishly complex allocator with a gazillion algorithms and approaches ( and a huge binary), yet mimalloc (a simple allocator with one bitmap-tracked pool per allocation size, and one pool collection per thread) is one of the bigger wins in software simplicity in recent memory.
<a href="https://archive.ph/CFQBU" rel="nofollow">https://archive.ph/CFQBU</a>
I nice use case too<p><a href="https://technology.blog.gov.uk/2015/12/11/using-jemalloc-to-get-to-the-bottom-of-a-memory-leak/" rel="nofollow">https://technology.blog.gov.uk/2015/12/11/using-jemalloc-to-...</a>
Jemalloc and Jalad at Tanagra!
Surprised not to see any mention of the global memory supply shock. Would love to learn more about how that economic is shifting software priorities toward memory allocation for the first time in my (relatively young) career
While it may seem directly related, it's just not. These things are worked on regardless of how cheap or expensive RAM is, because optimizing memory footprint pretty much always leads to fewer machines leased, which is a worthwhile goal even for smaller shops.
There’s been shocks at hyperscaler scale, ex. this got yuge at Google for a couple years before ChatGPT
jemalloc saved my icinga2 installation that kept exploding in memory usage, when i (and agents from sub-zones) was hammering its api<p>when i preloaded jemalloc , memory remained at significantly lower levels, and - more importantly - it was stable.<p>there seems to be no single correct solution to memory allocation, depending on the workload
The only option for cookies is to accept these terms and conditions, I thought implied consent was explicitly not allowed due to GDPR?<p>"To help personalize content, tailor and measure ads and provide a safer experience, we use cookies. By clicking or navigating the site, you agree to allow our collection of information on and off Facebook through cookies. Learn more, including about available controls:<p><a href="https://engineering.fb.com/privacy" rel="nofollow">https://engineering.fb.com/privacy</a>"
Glad to see the commitment towards important non-LLM projects!
Few months back, some of the services switched to jemalloc for the Java VM. It took months (of memory dumps and tracing sys-calls) to blame the JVM, itself, for getting killed by the oom_killer.<p>Initially the idea was diagnostics, instead the the problem disappeared on its own.
(wrong thread)
Large engineering orgs often underestimate how much CI pipelines amplify performance issues. Even small inefficiencies multiply when builds run hundreds of times a day.
Someone should tell Bryan Cantrill, he'd probably be ecstatic...
First impressions: LOL, the blunt commentary in the HN thread title compared to the PR-speak of the fb.com post.<p>Second thoughts: Actually the fb.com post is more transparent than I'd have predicted. Not bad at all. Of course it helps that they're delivering good news!
How is the original author making out in the new arrangement?
Jason Evans worked for Facebook for almost two decades, starting in 2009 - <a href="https://jasone.github.io/2025/06/12/jemalloc-postmortem/" rel="nofollow">https://jasone.github.io/2025/06/12/jemalloc-postmortem/</a><p>He's doing just fine. If you're looking for a story about a FAANG company not paying engineers well for their work, this isn't it.
I used jemalloc recently for ComfyUI/Wan and it’s literally magic. I’m surprised it doesn’t come that way by default.
> Building a software system is a lot like building a skyscraper: The product everyone sees is the top, but the part that keeps it from falling over is the foundation buried in the dirt and the scaffolding hidden from sight.<p>They should have just called it an ivory tower, as that's what they're building whenever they're not busy destroying democracy with OS Backdoor lobbyism or Cambridge Analytica shenanigans.<p>Edit: If every thread about any of Elon Musk's companies can contain at least 10 comments talking about Elon's purported crimes against humanity, threads about Zuckerberg's companies can contain at least 1 comment. Without reminders like this, stories like last week's might as well remain non-consequential.
>We are committed to continuing to develop jemalloc development<p>From the Department of Redundancy Department.
Jemalloc also is used by android bionic libc library
scudo has been the default allocator for Android since Android 11, and we are hoping to make it mandatory for the few remaining places that don't use it. Using an allocator without memory protections in 2026 (especially after we have closed nearly all known performance gaps with jemalloc) is really not a great choice.
Doesn't it depend on vendors/customization? Default is <a href="https://llvm.org/docs/ScudoHardenedAllocator.html" rel="nofollow">https://llvm.org/docs/ScudoHardenedAllocator.html</a> since Android 11 (2020).
I don't know, that is probably the case I guess?<p>I was recently debugging an app double-free segfault on my android 13 samsung galaxy A51 phone, and the internal stack trace pointed to jemalloc function calls (je_free).
Meta never abandoned jemalloc. <a href="https://github.com/facebook/jemalloc" rel="nofollow">https://github.com/facebook/jemalloc</a> remained public the entire time. It's my understanding that Jason Evans, the creator of jemalloc, had ownership over the jemalloc/jemalloc repo which is why that one stopped being updated after he left.
Seems like they’d want to wait to commit until after the layoffs, right?
I work in the space. This article would not have been published if the team responsible was on the chopping block
It's just one team with like 4 people. They can layoff a lot of staff from Metaverse.
[dead]
[dead]
[dead]
And the Oscar for most mealy-mouthed post of the year goes to…
We generally try to avoid corporate press releases for that reason, but is there a good third-party post to replace it with?<p><a href="https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sort=byDate&type=comment&query=corporate%20press%20release%20by:dang" rel="nofollow">https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...</a>
All the AI investment and their biggest news is commitment to Jemalloc
If you need to optimize the allocator you are doing it wrong.
That's a false dichotomy: you optimize both the application <i>and</i> the allocator.<p>A 0.5% improvement may not be a lot to you, but at hyperscaler scale it's well worth staffing a team to work on it, with the added benefit of having people on hand that can investigate subtle bugs and pathological perf behaviors.
Glad we have super slow allocators then
Exactly. No need to engineer an allocator. You only live once!<p><pre><code> void* malloc(size_t size) {
void *ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_ANON, -1, 0);
return (ptr == MAP_FAILED) ? NULL : ptr;
}
void free(void *ptr) { /* YOLO */ }
</code></pre>
/s