git: 5b07152f3ec3 - stable/14 - vfs: vntblinit(): Rework comments on the computation of 'kern.maxvnodes'

The branch stable/14 has been updated by olce:

URL: https://cgit.FreeBSD.org/src/commit/?id=5b07152f3ec3eea78958796b45594c5bd96c0bfb

commit 5b07152f3ec3eea78958796b45594c5bd96c0bfb
Author:     Olivier Certner <olce@FreeBSD.org>
AuthorDate: 2025-05-12 11:20:01 +0000
Commit:     Olivier Certner <olce@FreeBSD.org>
CommitDate: 2025-05-20 09:05:33 +0000

    vfs: vntblinit(): Rework comments on the computation of 'kern.maxvnodes'
    
    Remove the parts that describe what is already in the code formula.  Add
    hints about which of 'physvnodes'/'virtvnodes' takes precedence, and
    when 'desiredvnodes' becomes smaller than 'maxfiles'.  These were both
    computed analytically and verified experimentally.
    
    Reviewed by:    kib (older version)
    MFC after:      3 days
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D50310
    
    (cherry picked from commit bf8890c84bacd8b1acebb2cb9a0944b1bb102b68)
---
 sys/kern/vfs_subr.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index a640bede85b9..62ae987a3084 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -722,15 +722,15 @@ vntblinit(void *dummy __unused)
 	int cpu, physvnodes, virtvnodes;
 
 	/*
-	 * Desiredvnodes is a function of the physical memory size and the
-	 * kernel's heap size.  Generally speaking, it scales with the
-	 * physical memory size.  The ratio of desiredvnodes to the physical
-	 * memory size is 1:16 until desiredvnodes exceeds 98,304.
-	 * Thereafter, the
-	 * marginal ratio of desiredvnodes to the physical memory size is
-	 * 1:64.  However, desiredvnodes is limited by the kernel's heap
-	 * size.  The memory required by desiredvnodes vnodes and vm objects
-	 * must not exceed 1/10th of the kernel's heap size.
+	 * 'desiredvnodes' is the minimum of a function of the physical memory
+	 * size and another of the kernel heap size (UMA limit, a portion of the
+	 * KVA).
+	 *
+	 * Currently, on 64-bit platforms, 'desiredvnodes' is set to
+	 * 'virtvnodes' up to a physical memory cutoff of ~1674MB, after which
+	 * 'physvnodes' applies instead.  With the current automatic tuning for
+	 * 'maxfiles' (32 files/MB), 'desiredvnodes' becomes smaller than it at
+	 * ~5136MB.
 	 */
 	physvnodes = maxproc + pgtok(vm_cnt.v_page_count) / 64 +
 	    3 * min(98304 * 16, pgtok(vm_cnt.v_page_count)) / 64;