[PATCH] Free the DIFO for a probe once it is loaded

[PATCH] Free the DIFO for a probe once it is loaded

[Kris Van Hees]

When a lot of probes are being probed, keeping all DIFO around consumes
a lot of memory.  Once the BPF program is loaded, the DIFO can be freed.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
---
 libdtrace/dt_bpf.c         | 23 ++++++++++++++++-------
 libdtrace/dt_prov_uprobe.c | 22 +++++++++++++++-------
 2 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
index ccec8b43..56b6b01d 100644
--- a/libdtrace/dt_bpf.c
+++ b/libdtrace/dt_bpf.c
@@ -1339,6 +1339,7 @@ dt_bpf_load_progs(dtrace_hdl_t *dtp, uint_t cflags)
 	 */
 	dtrace_getopt(dtp, "destructive", &dest_ok);
 
+	dp = NULL;
 	for (prp = dt_list_next(&dtp->dt_enablings); prp != NULL;
 	     prp = dt_list_next(prp)) {
 		int		fd;
@@ -1353,28 +1354,36 @@ dt_bpf_load_progs(dtrace_hdl_t *dtp, uint_t cflags)
 			continue;
 
 		if (dt_link(dtp, prp, dp, NULL) == -1)
-			return -1;
+			goto fail;
 
 		DT_DISASM_PROG_LINKED(dtp, cflags, dp, stderr, NULL, prp->desc);
 
 		if (dp->dtdo_flags & DIFOFLG_DESTRUCTIVE &&
-		    dest_ok == DTRACEOPT_UNSET)
-			return dt_set_errno(dtp, EDT_DESTRUCTIVE);
+		    dest_ok == DTRACEOPT_UNSET) {
+			dt_set_errno(dtp, EDT_DESTRUCTIVE);
+			goto fail;
+		}
 
 		fd = dt_bpf_load_prog(dtp, prp, dp, cflags);
 		if (fd == -1)
-			return -1;
+			goto fail;
 
 		if (prp->prov->impl->attach)
 			rc = prp->prov->impl->attach(dtp, prp, fd);
 
 		if (rc < 0) {
 			close(fd);
-			return dt_attach_error(dtp, rc,
-					       prp->desc->prv, prp->desc->mod,
-					       prp->desc->fun, prp->desc->prb);
+			dt_attach_error(dtp, rc,
+					prp->desc->prv, prp->desc->mod,
+					prp->desc->fun, prp->desc->prb);
+			goto fail;
 		}
 	}
 
 	return 0;
+
+fail:
+	dt_difo_free(dtp, prp->difo);
+	prp->difo = NULL;
+	return -1;
 }
diff --git a/libdtrace/dt_prov_uprobe.c b/libdtrace/dt_prov_uprobe.c
index f60bdceb..8e7aa4b0 100644
--- a/libdtrace/dt_prov_uprobe.c
+++ b/libdtrace/dt_prov_uprobe.c
@@ -609,32 +609,40 @@ static int add_probe_uprobe(dtrace_hdl_t *dtp, dt_probe_t *prp)
 	/* Make program. */
 	dp = dt_construct(dtp, prp, cflags, NULL);
 	if (dp == NULL)
-		return 0;        // FIXME in dt_bpf_make_progs() this is a fatal error; should we do the same here?
+		return 0;
 	prp->difo = dp;
 
 	/* Load program. */
 	if (dt_link(dtp, prp, dp, NULL) == -1)
-		return 0;        // FIXME in dt_bpf_load_progs() this is a fatal error; should we do the same here?
+		goto fail;
 
 	dtrace_getopt(dtp, "destructive", &dest_ok);
 	if (dp->dtdo_flags & DIFOFLG_DESTRUCTIVE &&
-	    dest_ok == DTRACEOPT_UNSET)
-		return dt_set_errno(dtp, EDT_DESTRUCTIVE);
+	    dest_ok == DTRACEOPT_UNSET) {
+		dt_set_errno(dtp, EDT_DESTRUCTIVE);
+		goto fail;
+	}
 
 	fd = dt_bpf_load_prog(dtp, prp, dp, cflags);
 	if (fd == -1)
-		return 0;        // FIXME in dt_bpf_load_progs() this is a fatal error; should we do the same here?
+		goto fail;
 
 	if (prp->prov->impl->attach)
 		rc = prp->prov->impl->attach(dtp, prp, fd);
 
 	if (rc < 0) {
 		close(fd);
-		return dt_attach_error(dtp, rc, prp->desc->prv, prp->desc->mod,
-						prp->desc->fun, prp->desc->prb);
+		dt_attach_error(dtp, rc, prp->desc->prv, prp->desc->mod,
+					 prp->desc->fun, prp->desc->prb);
+		goto fail;
 	}
 
 	return 0;
+
+fail:
+	dt_difo_free(dtp, prp->difo);
+	prp->difo = NULL;
+	return 0;	// FIXME in dt_bpf_make_progs() this is a fatal error; should we do the same here?
 }
 
 static int add_probe_usdt(dtrace_hdl_t *dtp, dt_probe_t *prp)
-- 
2.45.2

Re: [PATCH] Free the DIFO for a probe once it is loaded

[Nick Alcock]

On 25 Jul 2025, Kris Van Hees verbalised:

> When a lot of probes are being probed, keeping all DIFO around consumes
> a lot of memory.  Once the BPF program is loaded, the DIFO can be freed.

DIFO? BPFO, surely :)

... the attached patch only seems to free anything new on failure, not
on after-loading.

> +fail:
> +	dt_difo_free(dtp, prp->difo);
> +	prp->difo = NULL;
> +	return -1;
[...]
> +fail:
> +	dt_difo_free(dtp, prp->difo);
> +	prp->difo = NULL;
> +	return 0;	// FIXME in dt_bpf_make_progs() this is a fatal error; should we do the same here?

Re: [PATCH] Free the DIFO for a probe once it is loaded

[Kris Van Hees]

On Fri, Jul 25, 2025 at 07:39:51PM +0100, Nick Alcock wrote:
> On 25 Jul 2025, Kris Van Hees verbalised:
> 
> > When a lot of probes are being probed, keeping all DIFO around consumes
> > a lot of memory.  Once the BPF program is loaded, the DIFO can be freed.
> 
> DIFO? BPFO, surely :)
> 
> ... the attached patch only seems to free anything new on failure, not
> on after-loading.

Oops, yes, will fix and send out a new one.

> > +fail:
> > +	dt_difo_free(dtp, prp->difo);
> > +	prp->difo = NULL;
> > +	return -1;
> [...]
> > +fail:
> > +	dt_difo_free(dtp, prp->difo);
> > +	prp->difo = NULL;
> > +	return 0;	// FIXME in dt_bpf_make_progs() this is a fatal error; should we do the same here?