On Mon, Mar 20, 2006 at 07:46:13PM +0000, Alex Hayward wrote: > On Mon, 20 Mar 2006, Jim C. Nasby wrote: > > > No, this is perfectly fine. Inactive memory in FreeBSD isn't the same as > > Free. It's the same as 'active' memory except that it's pages that > > haven't been accessed in X amount of time (between 100 and 200 ms, I > > think). When free memory starts getting low, FBSD will start moving > > pages from the inactive queue to the free queue (possibly resulting in > > writes to disk along the way). > > > > IIRC, Cache is the directory cache, and Buf is disk buffers, which is > > somewhat akin to shared_buffers in PostgreSQL. > > I don't believe that's true. I'm not an expert in FreeBSD's VM internals, > but this is how I believe it works: > > Active pages are pages currently mapped in to a process's address space. > > Inactive pages are pages which are marked dirty (must be written to > backing store before they can be freed) and which are not mapped in to a > process's address. They're still associated with a VM object of some kind Actually, a page that is in the inactive queue *may* be dirty. In fact, if you start with a freshly booted system (or one that's been recently starved of memory) and read in a large file, you'll see the inactive queue grow even though the pages haven't been dirtied. > - like part of a process's virtual address space or a as part of the cache > for a file on disk. If it's still part of a process's virtual address > space and is accessed a fault is generated. The page is then put back in > to the address mappings. > > Cached pages are like inactive pages but aren't dirty. Then can be either > re-mapped or freed immediately. > > Free pages are properly free. Wired pages are unswappable. Buf I'm not > sure about. It doesn't represent that amount of memory used to cache files > on disk, I'm sure of that. The sysctl -d description is 'KVA memory used > for bufs', so I suspect that it's the amount of kernel virtual address > space mapped to pages in the 'active', 'inactive' and 'cache' queues. > > -- > Alex Hayward > Seatbooker > > > ---------------------------(end of broadcast)--------------------------- > TIP 9: In versions below 8.0, the planner will ignore your desire to > choose an index scan if your joining column's datatypes do not > match > -- Jim C. Nasby, Sr. Engineering Consultant jnasby@xxxxxxxxxxxxx Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
