

https://github.com/Overv/vramfs
Oh, it’s a user space (FUSE) driver. I was rather hoping it was an out-of-tree Linux kernel driver, since using FUSE will: 1) always pass back to userspace, which costs performance, and 2) destroys any possibility of DMA-enabled memory operations (DPDK is a possible exception). I suppose if the only objective was to store files in VRAM, this does technically meet that, but it’s leaving quite a lot on the table, IMO.
If this were a kernel module, the filesystem performance would presumably improve, limited by how the VRAM is exposed by OpenCL (ie very fast if it’s just all mapped into PCIe). And if it was basically offering VRAM as PCIe memory, then this potentially means the VRAM can be used for certain RAM niche cases, like hugepages: some applications need large quantities of memory, plus a guarantee that it won’t be evicted from RAM, and whose physical addresses can be resolved from userspace (eg DPDK, high-performance compute). If such a driver could offer special hugepages which are backed by VRAM, then those application could benefit.
And at that point, on systems where the PCIe address space is unified with the system address space (eg x86), then it’s entirely plausible to use VRAM as if it were hot-insertable memory, because both RAM and VRAM would occupy known regions within the system memory address space, and the existing MMU would control which processes can access what parts of PCIe-mapped-VRAM.
Is it worth re-engineering the Linux kernel memory subsystem to support RAM over PCIe? Uh, who knows. Though I’ve always like the thought of DDR on PCIe cards. All technologies are doomed to reinvent PCIe, I think, said someone from Level1Techs.


Connection tracking might not be totally necessary for a reverse proxy mode, but it’s worth discussing what happens if connection tracking is disabled or if the known-connections table runs out of room. For a well-behaved protocol like HTTP(S) that has a fixed inbound port (eg 80 or 443) and uses TCP, tracking a connection means being aware of the TCP connection state, which the destination OS already has to do. But since a reverse proxy terminates a TCP connection, then the effort for connection tracking is minimal.
For a poorly-behaved protocol like FTP – which receives initial packets in a fixed inbound port but then spawns a separate port for outbound packers – the effort of connection tracking means setting up the firewall to allow ongoing (ie established) traffic to pass in.
But these are the happy cases. In the event of a network issue that affects an HTTP payload sent from your reverse proxy toward the requesting client, a mid-way router will send back to your machine an ICMP packet describing the problem. If your firewall is not configured to let all ICMP packets through, then the only way in would be if conntrack looks up the connection details from its table and allows the ICMP packet in, as “related” traffic. This is not dissimilar to the FTP case above, but rather than a different port number, it’s an entirely different protocol.
And then there’s UDP tracking, which is relevant to QUIC. For hosting a service, UDP is connectionless and so for any inbound packet we received on port XYZ, conntrack will permit an outbound packet on port XYZ. But that’s redundant since we presumably had to explicitly allow inbound port XYZ to expose the service. But in the opposite case, where we want to access UDP resources on the network, then an outbound packet to port ABC means conntrack will keep an entry to permit an inbound packet on port ABC. If you are doing lots of DNS lookups (typically using UDP), then that alone could swamp the con track table: https://kb.isc.org/docs/aa-01183
It may behoove you to first look at what’s filling conntrack’s table, before looking to disable it outright. It may be possible to specifically skip connection tracking for anything already explicitly permitted through the firewall (eg 80/443). Or if the issue is due to numerous DNS resolution requests from trying to look up spam sources IPs, then perhaps either the logs should not do a synchronous DNS lookup, or you can also skip connection tracking for DNS.