svn commit: r327168 - head/sys/vm

[Peter Holm]

On Sun, Dec 24, 2017 at 07:45:16PM +0000, Mark Johnston wrote:
> Author: markj
> Date: Sun Dec 24 19:45:16 2017
> New Revision: 327168
> URL: https://svnweb.freebsd.org/changeset/base/327168
> 
> Log:
>   Fix two problems with the page daemon control loop.
>   
>   Both issues caused the page daemon to erroneously go to sleep when
>   applications are consuming free pages at a high rate, leaving the
>   application threads blocked in VM_WAIT.
>   
>   1) After completing an inactive queue scan, concurrent allocations may
>      have prevented the page daemon from meeting the v_free_min threshold.
>      In this case, the page daemon was going to sleep even when the
>      inactive queue contained plenty of clean pages.
>   2) pagedaemon_wakeup() may be called without the free queues lock held.
>      This can lead to a lost wakeup if a call occurs after the page daemon
>      clears vm_pageout_wanted but before going to sleep.
>   
>   Fix 1) by ensuring that we start a new inactive queue scan immediately
>   if v_free_count < v_free_min after a prior scan.
>   
>   Fix 2) by adding a new subroutine, pagedaemon_wait(), called from
>   vm_wait() and vm_waitpfault(). It wakes up the page daemon if either
>   vm_pages_needed or vm_pageout_wanted is false, and atomically sleeps
>   on v_free_count.
>   
>   Reported by:	jeff
>   Reviewed by:	alc
>   MFC after:	2 weeks
>   Differential Revision:	https://reviews.freebsd.org/D13424
> 
> Modified:
>   head/sys/vm/vm_page.c
>   head/sys/vm/vm_pageout.c
>   head/sys/vm/vm_pageout.h
> 

I now see threads blocked in VM_WAIT?

https://people.freebsd.org/~pho/stress/log/mark013.txt

- Peter