Re: Is Parallel Programming Hard, And, If So, What Can You Do About It?

On Mon, 19 May 2025 23:33:42 +0000, MitchAlsup1 wrote:

On Mon, 19 May 2025 1:13:01 +0000, Lawrence D'Oliveiro wrote:
 

Filesystem cache turnover happens in times on the order of seconds, not
milliseconds.

 
Yes, running at the latency and bandwidth of the disk/SSD subsystem not
of the DRAM system.

It’s not really about latency, it’s just about the way the filesystem
caches are used. They quite typically take up a big chunk of the RAM on a
server, and stuff does tend to hang around in them for several seconds, to
get good cache hits. (Though on Linux that’s considered a low-priority
use, so if a regular application needs more RAM and there isn’t enough
free, then the filesystem cache will be quickly flushed as necessary to
make more available.)

And consider that modern high-performance servers are available with
terabytes of RAM. Fill a few tens of % of that with filesystem cache, and
you see why disk caches don’t stand a chance.