how to recycle Inact memory more aggressively?

[Ian Lepore]

On Sun, 2016-03-13 at 19:08 -0700, Adrian Chadd wrote:
> On 13 March 2016 at 18:51, Mark Johnston <markj at freebsd.org> wrote:
> > On Sun, Mar 13, 2016 at 06:33:46PM -0700, Adrian Chadd wrote:
> > > Hi,
> > > 
> > > I can reproduce this by doing a mkimage on a large destination
> > > file
> > > image. it looks like it causes all the desktop processes to get
> > > paged
> > > out whilst it's doing so, and then the whole UI freezes until it
> > > catches up.
> > 
> > mkimg(1) maps the destination file with MAP_NOSYNC, so if it's
> > larger
> > than RAM, I think it'll basically force the pagedaemon to write out
> > the
> > image as it tries to reclaim pages from the inactive queue. This
> > can
> > cause stalls if the pagedaemon blocks waiting for some I/O to
> > complete.
> > The user/alc/PQ_LAUNDRY branch helps alleviate this problem by
> > using a
> > different thread to launder dirty pages. I use mkimg on various
> > desktop
> > machines to build bhyve images and have noticed the problem you're
> > describing; PQ_LAUNDRY helps quite a bit in that case. But I don't
> > know
> > why this would be a new problem.
> > 
> 
> That's why I'm confused. I just know that it didn't used to cause the
> whole UI to hang due to paging.
> 

I've been noticing this too.  This machine runs 10-stable and this use
of the swap began happening recently when I updated from 10-stable
around the 10.2 release time to 10-stable right about when the 10.3
code freeze began.

In my case I have no zfs anything here.  I noticed the problem bigtime
yesterday when rsync was syncing a ufs filesystem of about 500GB from
one disk to another (probably 70-80 GB actually needed copying).  My
desktop apps were noticibly unresponsive when I activated a window that
had been idle for a while (like it would take a couple seconds for the
app to begin responding).  I could see lots of swap In happening in top
during this unresponsiveness, and noticible amounts of Out activity
when nothing was happening except the rsync.

This is amd64, 12GB ram, 16GB swap, a tmpfs had about 400MB in it at
the time.  Prior to the update around the 10.3 freeze, this machine
would never touch the swap no matter what workload I threw at it (this
rsync stuff happens every day, it's the usual workload).

-- Ian