git: kernel - Major refactor of pageout daemon algorithms (2)
dillon at crater.dragonflybsd.org
Mon May 17 23:11:08 PDT 2021
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date: Mon May 17 21:57:37 2021 -0700
kernel - Major refactor of pageout daemon algorithms (2)
* Refactor the pageout daemon's 'pass' variable handling. No longer
sleep or slow down the pageout daemon if paging has been running for
a long time, doing so just places the system in an unrecoverable
* Fix a vm_paging_target2() test that was inverted. This caused the
vm_pageout_scan_inactive() to improperly break out after scanning
one page per queue (x 1024 queues so it wasn't readily apparent).
* Modify the 'vmwait' and 'pfault' trip points (that block a process on
low memory) based on the process nice value. The result is that nice +N
processes which are heavy memory users will tend to block before
completely exhausting the FREE+CACHE pool, allowing other lower-niced
processes to continue running somewhat normally.
I say somewhat because the mechanism isn't perfect. However, it should
be good enough that if bulk work is partitioned a bit with higher nice
values, shells should remain responsive enough to diagnose issues even
during extreme paging.
* For the moment make the 'vmwait' trip point only slightly worse
than the 'pfault' trip point at any given p_nice. The 'vmwait' trip
point used to be significantly worse (that is, would trip earlier).
We have generally found that blockages on pfault are significantly more
damaging to performance than blockages on I/O-related allocations, so
don't completely equalize the two trip points.
* Have the pageout code check for and report possible vm_page queue
races when removing pages. In particular, pages appear to be able
to wind up in PQ_CACHE that are still PG_MAPPED.
* Fix various calculations that divide by MAXSCAN_DIVIDER to error
on the high-side instead of the low-side.
* Fix vm.pageout_debug output to reduce spew.
Summary of changes:
sys/vm/vm_page.c | 39 ++++++++++++++---
sys/vm/vm_page2.h | 27 ++++++++++++
sys/vm/vm_pageout.c | 120 +++++++++++++++++++++++++++++++---------------------
3 files changed, 130 insertions(+), 56 deletions(-)
DragonFly BSD source repository
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