21–30 of 73 posts
Doing research though a spinlock actually doesn't seem as unusual a hack as it would first seem, do drivers and the like not have similar issues because they don't trigger a page fault I guess?
It only took a few decades for Linux to get a good CPU scheduler and good I/O schedulers, too. I don't get how such an important area can be so bad for so long. But then, bad scheduling is everywhere. I find it to be a pretty fun area to work in, but, judging by how much it is less than half-assed in much existing software, most developers seem to hate dealing with it?
It is a crime that postgres isn't able to allocate with 1GB huge pages by changing a config parameter in 2026 Also a crime that people are still running databases with 4kb pages. To put it in perspective, this means you will have more than 30 million pages on a server with 128GB RAM. As an example, if there is 16bytes of metadata for memory page. The metadata itself would take more than half a gigabyte.
It is a crime that postgres isn't able to allocate with 1GB huge pages by changing a config parameter in 2026 Also a crime that people are still running databases with 4kb pages. To put it in perspective, this means you will have more than 30 million pages on a server with 128GB RAM. As an example, if there is 16bytes of metadata for memory page. The metadata itself would take more than half a gigabyte.
Seems Linus needs to yell at someone again. Especially with containers around you might very well hit the case of running new kernel but older version of PostgreSQL with no code mitigation for the problem
I'd rather like to know if any real world usage broke, before coming to the conclusion that an edge case synthetic benchmark is worth changing the kernel (back or wherever) where supposedly the change that broke the benchmark had real world benefits. Since we will never know it might be a good idea to feature gate the change, change the default and let users decide to change it back. This may give some feedback on th…
"synthetic benchmark" is doing some heavy lifting here. Pgbench just runs a bunch of SQL statements against a real Postgres instance. It's very close to a real world simulation of a production workload
For example, this issue aside, I'd rather split such a workload into multiple smaller instances, naturally. Because the impact of a crash on this single node, heavy load, many cores, many clients scenario would be huge.
Seems Linus needs to yell at someone again. Especially with containers around you might very well hit the case of running new kernel but older version of PostgreSQL with no code mitigation for the problem
I get that folks love a good Linus rant. But as someone who's been at the end of that style of "feedback", nothing can be more humiliating or demotivating. Certainly there are contributors that are making "rookie mistakes". There are folks that aren't willing to ingest the entire context of what was tried back in 2.0.36, 2.2, 2.4... etc. And perhaps it's wise to simply stay away until you're completely certain you've…
Would you be able to point one out?
> to well-intentioned contributors
This is a system used and relied upon by billions of people around the world. Your intentions, while good, are not material to the problem. Put another way we have an endless supply of people with "good intentions" but we don't enjoy the same largess of people with "good skills."
PREEMPT_LAZY triggering on page faults seems like a bad idea in light of this. It is probably not a good idea to suspend processes right when they get unexpectedly bogged down. The logic makes a little more sense for syscalls that are expected to take long compared to a scheduling quantum (a few milliseconds). But page faults are mostly invisible and unplannable. It only took a few decades for Linux to get a good CPU…
What if it was on a VM and the core holding the lock got descheduled from the hypervisor?
This post comes uncomfortably close to plagiarizing https://thebuild.com/blog/2026/04/23/preempt_none-is-dead-yo... , which it cites as a source; almost all the technical explanation is in there and some of the wording is extremely similar. Compare, e.g., "What Linux 7.0 actually changed" in Pettus's post to "What Is Preemption?" in this one. I think this link should have been to Pettus's post instead.