Messages in this thread | | | Date | Thu, 16 Oct 2003 13:44:40 +0200 | From | Jakob Oestergaard <> | Subject | Re: About _real_ free memory |
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On Thu, Oct 16, 2003 at 11:04:14AM +0200, Frederick, Fabian wrote: > If a process tries to allocate and use more than the really free > amount, some cache will be dropped automatically. From a performance > point of view, this could of course be undesirable, but normally > there's no need to think about it. > > <Why don't we have a command to drop some cache ? or maybe some > <kernel rules to do it ? we could gain some more scalability doing that kind > of > <stuff during low load.
No - you would throw out disk cache with the risk of throwing out potentially useful data. The data can be thrown out *immediately* anyway if someone needs it.
So: gain: zero loss: likely noticable ------------------------------ total: bad idea
>Another problem is end-user point of view : > > < -What's available on a box before swapping ? > < -Do I have to add RAM right now ?
[albatross:joe] $ free total used free shared buffers cached Mem: 1033944 902036 131908 0 41120 446456 -/+ buffers/cache: 414460 619484 Swap: 2101000 294552 1806448
I have 619 MB of free memory now, if you do not count in the caches.
The free physical memory is around 132 MB - this number tells me how much memory the kernel could not find a use for (for either processes or cache) - e.g. the amount of memory that I paid for but is not doing anything useful.
You want the physical free memory to be as low as possible - it is the amount of memory that is being wasted in the system by not doing anything useful. If the user cannot understand this, they should learn not to care either. Certainly, you should never ruin the workings of the VM subsystem by freeing useful cache memory, just so a user who has no understanding of what is actually going on, can get a nice big number in his 'free' output.
Maybe one could patch the 'free' utility instead? ;)
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