Re: Strange ARC/Swap/CPU on yesterday's -CURRENT

On 05/04/2018 05:03, Mark Millard wrote:
> I've classically seen things like (picking on java here):
> (no patch yet, so SWAP 0K shows)
> 
>   PID USERNAME       THR PRI NICE   SIZE    RES   SWAP STATE   C   TIME     CPU COMMAND
> 78694 root            44  52    0 14779M 92720K     0K uwait  22   0:06   9.91% [java]
> 
> when Swap: . . . 0 Used . . . (or some figure much
> smaller than SIZE-RES) showed. (SIZE is ki_size and
> RES is ki_rssize as I remember.) It suggests some
> form of reserved-but-not-allocated contribution to
> ki_size (SIZE), space not resident nor swapped out
> to a swap partition. Possibly vnode-backed (potential
> "VN PAGER in and out" contributions instead of "SWAP
> PAGER" ones, in systat -vmstat terms)?
> 
> Are such cases examples of what you were counting
> as "wildly inaccurate"? Or do you count vnode-backed
> but not resident as perfectly good examples of SWAP
> in use?

Apologies, but I didn't quite get your question...

Instead, I think I now understand better what top actually reports.
I think that it reports swap usage based on the archaic swapout algorithm where
a whole process is moved to swap when a memory shortage arises.  And then the
process can be gradually swapped in.  So, ki_swrss - ki_rssize is an estimate of
how much process's memory still left in swap (the difference between the
resident size before the full swapout and the current resident size).
Of course, now we have the modern swapout where individual inactive dirty
anonymous pages can be paged out to swap (the classic whole-process swapout
still can happen, but is quite rare), but top is not aware of that.

-- 
Andriy Gapon