bump maxthreads default and on amd64.

bump the default MAXLWP to 4096 from 2048, and adjust the default
threads seen to be 2048 cur / 4096 max.  remove the linkage to
maxuprc entirely.

implement cpu_maxlwp() on amd64 to grow beyond the default when
a lot of memory is available, picking 1 lwp per 1MiB of ram,
limited to 65535 like the system limit.


i've been having weird firefox issues for a few months now and
it turns out i was having pthread_create() failures and since
bumping the defaults i've had none of the recent issues.


Index: sys/arch/amd64/amd64/process_machdep.c
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/amd64/process_machdep.c,v
retrieving revision 1.49
diff -p -u -r1.49 process_machdep.c
--- sys/arch/amd64/amd64/process_machdep.c	19 Oct 2020 17:47:37 -0000	1.49
+++ sys/arch/amd64/amd64/process_machdep.c	1 May 2022 04:25:42 -0000
@@ -432,3 +432,16 @@ process_machdep_validfpu(struct proc *p)
 	return 1;
 }
 #endif /* __HAVE_PTRACE_MACHDEP */
+
+#ifdef __HAVE_CPU_MAXLWP
+int
+cpu_maxlwp(void)
+{
+	/* Assume 1 LWP per 1MiB, system max is 65535. */
+	const int min_lwps = 4096;
+	const int max_lwps = 65535;
+	uint64_t lwps_per = ctob(physmem) / (1024 * 1024);
+
+	return MAX(MIN(max_lwps, lwps_per), min_lwps);
+}
+#endif /* __HAVE_CPU_MAXLWP */
Index: sys/arch/amd64/include/types.h
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/include/types.h,v
retrieving revision 1.71
diff -p -u -r1.71 types.h
--- sys/arch/amd64/include/types.h	1 Apr 2021 04:35:45 -0000	1.71
+++ sys/arch/amd64/include/types.h	1 May 2022 04:25:42 -0000
@@ -101,6 +101,7 @@ typedef	unsigned char		__cpu_simple_lock
 #define	__HAVE_MM_MD_DIRECT_MAPPED_PHYS
 #define	__HAVE_UCAS_FULL
 #define	__HAVE_BUS_SPACE_8
+#define	__HAVE_CPU_MAXLWP
 
 #ifdef _KERNEL_OPT
 #define	__HAVE_RAS
Index: sys/kern/kern_proc.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_proc.c,v
retrieving revision 1.266
diff -p -u -r1.266 kern_proc.c
--- sys/kern/kern_proc.c	7 Apr 2022 19:33:38 -0000	1.266
+++ sys/kern/kern_proc.c	1 May 2022 04:25:42 -0000
@@ -539,7 +539,7 @@ proc0_init(void)
 	rlim[RLIMIT_MEMLOCK].rlim_cur = lim / 3;
 
 	rlim[RLIMIT_NTHR].rlim_max = maxlwp;
-	rlim[RLIMIT_NTHR].rlim_cur = maxlwp < maxuprc ? maxlwp : maxuprc;
+	rlim[RLIMIT_NTHR].rlim_cur = maxlwp / 2;
 
 	/* Note that default core name has zero length. */
 	limit0.pl_corename = defcorename;
Index: sys/sys/lwp.h
===================================================================
RCS file: /cvsroot/src/sys/sys/lwp.h,v
retrieving revision 1.215
diff -p -u -r1.215 lwp.h
--- sys/sys/lwp.h	9 Apr 2022 23:45:37 -0000	1.215
+++ sys/sys/lwp.h	1 May 2022 04:25:42 -0000
@@ -239,9 +239,11 @@ extern struct lwplist	alllwp;		/* List o
 extern lwp_t		lwp0;		/* LWP for proc0. */
 extern int		maxlwp __read_mostly;	/* max number of lwps */
 #ifndef MAXLWP
-#define	MAXLWP		2048
+#define	MAXLWP		4096
 #endif
-#ifndef	__HAVE_CPU_MAXLWP
+#ifdef	__HAVE_CPU_MAXLWP
+int cpu_maxlwp(void);
+#else
 #define	cpu_maxlwp()	MAXLWP
 #endif
 #endif