Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list)

[David Howells]

David Hildenbrand <david@xxxxxxxxxx> wrote:

> >> percpu counters maybe - add them up at the point of viewing?
> > They are percpu, see my last email. But for every 108 changes (on
> > my system), they will do two atomic_long_adds(). So not very
> > useful for anything but low frequency modifications.
> > 
> 
> Can we just treat the whole acquired/released accounting as a debug mechanism
> to detect missing releases and do it only for debug kernels?
> 
> 
> The pcpu counter is an s8, so we have to flush on a regular basis and cannot
> really defer it any longer ... but I'm curious if it would be of any help to
> only have a single PINNED counter that goes into both directions (inc/dec on
> pin/release), to reduce the flushing.
> 
> Of course, once we pin/release more than ~108 pages in one go or we switch
> CPUs frequently it won't be that much of a help ...

What are the stats actually used for?  Is it just debugging, or do we actually
have users for them (control groups spring to mind)?

David