PR/58666 CVS commit: [netbsd-10] src/sys/kern

["Martin Husemann" <martin%netbsd.org@localhost>]

The following reply was made to PR kern/58666; it has been noted by GNATS.

From: "Martin Husemann" <martin%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/58666 CVS commit: [netbsd-10] src/sys/kern
Date: Sun, 15 Dec 2024 14:58:46 +0000

 Module Name:	src
 Committed By:	martin
 Date:		Sun Dec 15 14:58:45 UTC 2024
 
 Modified Files:
 	src/sys/kern [netbsd-10]: subr_pool.c
 
 Log Message:
 Pull up following revision(s) (requested by chs in ticket #1028):
 
 	sys/kern/subr_pool.c: revision 1.292
 
 pool: fix pool_sethiwat() to actually do something
 
 The change that I made to the pool code back in April 2020
 ("slightly change and fix the semantics of pool_set*wat()" ...)
 accidental broke pool_sethiwat() by making it have no effect.
 
 This was discovered after the crash reported in PR 58666 was fixed.
 
 The same machine (32-bit, with 10GB RAM) would hang due to the buffer
 cache causing the system to run out of kernel virtual space.  The
 buffer cache uses a separate pool for buffer data for each power of 2
 between DEV_BSIZE and MAXBSIZE, and if the usage pattern of buffer
 sizes changes then memory has to be moved between the different pools
 in order to create buffers of the new size.  The buffer cache handles
 this by using pool_sethiwat() to cause memory freed from the buffer
 cache back to the pools to not be cached in the buffer cache pools but
 instead be freed back to the pools' back-end allocator (which
 allocates from the low-level kva allocator) as soon as possible.  But
 since pool_sethiwat() wasn't doing anything, memory would stay cached
 in some buffer cache pools and starve other buffer cache pools (and a
 few other pools that do no use the kmem layer for memory allocation).
 
 Fix pool_sethiwat() to do what it is supposed to do again.
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.285.4.1 -r1.285.4.2 src/sys/kern/subr_pool.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.