Home/ Questions/Q 7076503
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-28T06:18:21+00:00

(Don’t know if this is strictly on-topic, but I don’t see any better Stack

  • 0

(Don’t know if this is strictly on-topic, but I don’t see any better Stack Exchange site for it.)

My Linux development machine has a limited amount of memory (so to speak — 2.5GB doesn’t seem like much of a limitation to me). The first time I try to compile any piece of my small-to-mid-sized project, I get three to five minutes (yes, minutes) of IOWait delay before it actually does any compiling. Once it gets done reading whatever it’s reading, the compile itself takes mere seconds.

If that were all, I’d just grin and bear it, but if I do essentially anything between compiles — even just switching to a Firefox window for a few minutes of research — I get the same delay again. It’s hard to stay focused through such long thumb-twiddling sessions.

The system is using more than a gigabyte of disk cache. My carefully-crafted precompiled header file is only a little more than 200MB — large, but not large enough to overflow the cache. What is GCC looking for that takes so freakin’ long?! Or alternatively, how can I find out? GCC has a bewildering array of debugging options, but none of them seem to show what files it’s looking at.

Any pointers would be appreciated.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    I couldn’t figure out any way to determine what it was looking at, but I did find a solution.

    Reducing the cache-pressure from 100 to 10 (with the command sudo sysctl -w vm.vfs_cache_pressure=10) helped a great deal, by telling the system to keep file-system data in the cache in preference to file contents; it kept the time to compile a single test cpp file down to 16 seconds, even after several hours.

    But after leaving the system running overnight, compiling it went back to 3:18 the first time, and only dropped to 1:04 the second (and 1:01 the third); the only difference was that other parts of the system had grabbed more memory overnight. So I bit the bullet and allocated about half-gigabyte of memory to it… with the cache-pressure setting, that seems to have completely solved the problem.

    I’d still like to know exactly what it’s reading so much of, that more than a gigabyte of cache memory couldn’t hold it all, but this will suffice for now.

    • 0