git: 7fdf0e883567 - main - dtrace: add a knob to control maximum size of principal buffers

The branch main has been updated by avg:

URL: https://cgit.FreeBSD.org/src/commit/?id=7fdf0e883567d96d27d929c49a74d5fdb84d550b

commit 7fdf0e883567d96d27d929c49a74d5fdb84d550b
Author:     Andriy Gapon <avg@FreeBSD.org>
AuthorDate: 2022-01-11 13:44:46 +0000
Commit:     Andriy Gapon <avg@FreeBSD.org>
CommitDate: 2022-01-11 13:47:50 +0000

    dtrace: add a knob to control maximum size of principal buffers
    
    We had a hardcoded limit of 1/128-th of physical memory that was further
    subdivided between all CPUs as principal buffers are allocated on the
    per-CPU basis.  Actually, the buffers could use up 1/64-th of the
    memmory because with the default switch policy there are two buffers per
    CPU.
    
    This commit allows to change that limit.
    
    Note that the discussed limit is per dtrace command invocation.
    The idea is to limit the size of a single malloc(9) call, not the total
    memory size used by DTrace buffers.
    
    Reviewed by:    markj
    MFC after:      3 weeks
    Differential Revision:  https://reviews.freebsd.org/D33648
---
 sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c | 4 +++-
 sys/cddl/dev/dtrace/dtrace_sysctl.c                     | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
index 4798db98f6fe..38612a088066 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
@@ -207,6 +207,7 @@ hrtime_t	dtrace_deadman_user = (hrtime_t)30 * NANOSEC;
 hrtime_t	dtrace_unregister_defunct_reap = (hrtime_t)60 * NANOSEC;
 #ifndef illumos
 int		dtrace_memstr_max = 4096;
+int		dtrace_bufsize_max_frac = 128;
 #endif
 
 /*
@@ -12205,7 +12206,8 @@ err:
 	 * ask to malloc, so let's place a limit here before trying
 	 * to do something that might well end in tears at bedtime.
 	 */
-	if (size > physmem * PAGE_SIZE / (128 * (mp_maxid + 1)))
+	int bufsize_percpu_frac = dtrace_bufsize_max_frac * mp_ncpus;
+	if (size > physmem * PAGE_SIZE / bufsize_percpu_frac)
 		return (ENOMEM);
 #endif
 
diff --git a/sys/cddl/dev/dtrace/dtrace_sysctl.c b/sys/cddl/dev/dtrace/dtrace_sysctl.c
index 8473c549ddc2..db2c44db0249 100644
--- a/sys/cddl/dev/dtrace/dtrace_sysctl.c
+++ b/sys/cddl/dev/dtrace/dtrace_sysctl.c
@@ -96,5 +96,9 @@ SYSCTL_QUAD(_kern_dtrace, OID_AUTO, dof_maxsize, CTLFLAG_RW,
 SYSCTL_QUAD(_kern_dtrace, OID_AUTO, helper_actions_max, CTLFLAG_RW,
     &dtrace_helper_actions_max, 0, "maximum number of allowed helper actions");
 
+SYSCTL_INT(_kern_dtrace, OID_AUTO, bufsize_max, CTLFLAG_RWTUN,
+    &dtrace_bufsize_max_frac, 0,
+    "maximum fraction (1/n-th) of physical memory for principal buffers");
+
 SYSCTL_INT(_security_bsd, OID_AUTO, allow_destructive_dtrace, CTLFLAG_RDTUN,
     &dtrace_allow_destructive, 1, "Allow destructive mode DTrace scripts");