On 05/29/2012 03:29 AM, Daniel Carosone wrote:
For the mmap case: does the ARC keep a separate copy, or does the vm system map the same page into the process's address space? If a separate copy is made, that seems like a potential source of many kinds of problems - if it's the same page then the whole premise is essentially moot and there's no "double caching".

As far as I understand, for mmap case, is that the page cache is distinct from ARC (i.e. normal simplified flow for reading from disk with mmap is DSK->ARC->PageCache) - and only page cache gets mapped into processes address space - which is what results in the double caching.

I have two other general questions regarding page cache with ZFS + Solaris:
 - Does anything else except mmap still use the page cache ?
- Is there a parameter similar to /proc/sys/vm/swappiness that can control how long unused pages in page cache stay in physical ram if there is no shortage of physical ram ? And if not how long will unused pages stay in page cache stay in physical ram given there is no shortage of physical ram ?
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