linux-kernel - [PATCH] kbuild,bpf: pass make jobs' value to pahole

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Message-ID: <20241102100452.793970-1-flo@geekplace.eu>
Date: Sat,  2 Nov 2024 11:04:51 +0100
From: Florian Schmaus <flo@...kplace.eu>
To: Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>
Cc: Florian Schmaus <flo@...kplace.eu>,
	bpf@...r.kernel.org,
	linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] kbuild,bpf: pass make jobs' value to pahole

Pass the value of make's -j/--jobs argument to pahole, to avoid out of
memory errors and make pahole respect the "jobs" value of make.

On systems with little memory but many cores, invoking pahole using -j
without argument potentially creates too many pahole instances,
causing an out-of-memory situation. Instead, we should pass make's
"jobs" value as an argument to pahole's -j, which is likely configured
to be (much) lower than the actual core count on such systems.

If make was invoked without -j, either via cmdline or MAKEFLAGS, then
JOBS will be simply empty, resulting in the existing behavior, as
expected.

Signed-off-by: Florian Schmaus <flo@...kplace.eu>
---
 scripts/Makefile.btf | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
index b75f09f3f424..c3cbeb13de50 100644
--- a/scripts/Makefile.btf
+++ b/scripts/Makefile.btf
@@ -3,6 +3,8 @@
 pahole-ver := $(CONFIG_PAHOLE_VERSION)
 pahole-flags-y :=
 
+JOBS := $(patsubst -j%,%,$(filter -j%,$(MAKEFLAGS)))
+
 ifeq ($(call test-le, $(pahole-ver), 125),y)
 
 # pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
@@ -12,14 +14,14 @@ endif
 
 pahole-flags-$(call test-ge, $(pahole-ver), 121)	+= --btf_gen_floats
 
-pahole-flags-$(call test-ge, $(pahole-ver), 122)	+= -j
+pahole-flags-$(call test-ge, $(pahole-ver), 122)	+= -j$(JOBS)
 
 pahole-flags-$(call test-ge, $(pahole-ver), 125)	+= --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
 
 else
 
 # Switch to using --btf_features for v1.26 and later.
-pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
+pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
 
 ifneq ($(KBUILD_EXTMOD),)
 module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base
-- 
2.45.2