On Wed, 24 Jan 2007 18:41:27 -0800 (PST)
Christoph Lameter <[email protected]> wrote:
> > But I can't think of the way to show that.
> > ==
> > [kamezawa@aworks src]$ free
> > total used free shared buffers cached
> > Mem: 741604 724628 16976 0 62700 564600
> > -/+ buffers/cache: 97328 644276
> > Swap: 1052216 2532 1049684
> > ==
>
> Could we call the free memory "unused memory" and not talk about free
> memory at all?
>
Ah, maybe it's better.
I met several memory troubles in user's systems in these days. (on older kernels)
Thousands/hundreds of process works on it.
When I explain the cutomers about memory management, I devides memory into..
(1) unused memory --- memory which is not used, in free-list of zones.
(2) reclaimable memory --- page cache, which is reclaimable
clean pages --- can be reclaimed soon
dirty pages --- need to be written back
*BUT* busy pages are unreclaimable.
(3) swappable memory --- user process's pages. basically reclaimable if
swap is available.
shmem pages are included here.
(4) locked memory --- mlocked memory, which is not reclaimable(but movable)
(5) kernel memory --- used by kernel,
(and we can't see how many pages are reclaimable)
We can know the amount of (1) and (5) and total memory.
Basically, (3) = (Total) - (2) - (1).
busy data-set of (2)(3) is not reclaimable. but the amount of busy data-set
is unknown. Many users takes log of 'ps' or 'sar' to estimate their memory
usage. (and sometimes page-cache of 'log-file' eats their memory.....)
The amount of (4) is unknown. But there was a system with 6GB of 8GB
memory was mlocked (--; and OOM works.
I'm sorry that I can't catch up how the current kernel can show memory usage.
I should investigate that.
FYI:
Because some customers are migrated from mainframes, they want to control
almost all features in OS, IOW, designing memory usages.
-Kame
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