Re: kern/56309 (swapctl -U is very inefficient (takes ages to eternities))

[jdolecek%NetBSD.org@localhost]

Synopsis: swapctl -U is very inefficient (takes ages to eternities)

State-Changed-From-To: open->analyzed
State-Changed-By: jdolecek%NetBSD.org@localhost
State-Changed-When: Sat, 03 Aug 2024 17:48:44 +0000
State-Changed-Why:
The swapoff code reuses fault mechanics. That code path is synchronous
and reading 1 memory page at a time. This effectively means the swapoff
is synchronously reading data from the drive with 1 request for each 4KB.

Secondary problem is that the swslots for each amap are processed
in increasing order, which happen to use decreasing disk blocks.
This might defeat drive disk cache if the drive caches the blocks after
the requested block, but not onces before.

The main problem is the synchronous reads. I'll check if that path can
be changed to be asynchronous for the amap reads.