How to set maximum disk cache size?

Bruce Cran bruce at
Fri Nov 16 16:03:18 PST 2007

Ivan Voras wrote:
> On 16/11/2007, Laszlo Nagy <gandalf at> wrote:
>> Ivan Voras wrote:
>> I read this too but I don't understand. Too difficult for me.
>> So what is the answer? Do I need to set a sysctl or will FreeBSD use all
>> available free memory for caching file data from disk?
> You don't need to change anything, it's the default state.

So as long as the memory isn't shown as "Free" in top, any memory that 
isn't being used by the kernel or by applications is being used for 
cache/buffer?  One reason why I had thought that FreeBSD didn't use all 
the memory for caching disk accesses was because I saw a different 
behaviour when decompressing large archives between Linux and FreeBSD: 
in Linux there's a massive burst of activity as the archive gets put 
straight into memory; then, once memory starts getting full it pauses 
for what seems a very long time as it flushes all the data to disk. 
FreeBSD doesn't seem to do that; it seems a lot smoother in that it 
writes to the disk a lot more regularly - is this likely to be because 
Linux has a higher limit on the number of dirty pages it can have in 
memory before it writes them out to disk?


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