[PATCH v6 15/37] lib: introduce early boot parameter to avoid page_ext memory overhead

Suren Baghdasaryan
2024-03-21T16:37:43Z

The highest memory overhead from memory allocation profiling comes from
page_ext objects. This overhead exists even if the feature is disabled
but compiled-in. To avoid it, introduce an early boot parameter that
prevents page_ext object creation. The new boot parameter is a tri-state
with possible values of 0|1|never. When it is set to "never" the
memory allocation profiling support is disabled, and overhead is minimized
(currently no page_ext objects are allocated, in the future more overhead
might be eliminated). As a result we also lose ability to enable memory
allocation profiling at runtime (because there is no space to store
alloctag references). Runtime sysctrl becomes read-only if the early boot
parameter was set to "never". Note that the default value of this boot
parameter depends on the CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT
configuration. When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n
the boot parameter is set to "never", therefore eliminating any overhead.
CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y results in boot parameter
being set to 1 (enabled). This allows distributions to avoid any overhead
by setting CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n config and
with no changes to the kernel command line.
We reuse sysctl.vm.mem_profiling boot parameter name in order to avoid
introducing yet another control. This change turns it into a tri-state
early boot parameter.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
lib/alloc_tag.c | 41 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index cb5adec4b2e2..617c2fbb6673 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -116,9 +116,46 @@ static bool alloc_tag_module_unload(struct codetag_type *cttype,
return module_unused;
}

+#ifdef CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT
+static bool mem_profiling_support __meminitdata = true;
+#else
+static bool mem_profiling_support __meminitdata;
+#endif
+
+static int __init setup_early_mem_profiling(char *str)
+{
+ bool enable;
+
+ if (!str || !str[0])
+ return -EINVAL;
+
+ if (!strncmp(str, "never", 5)) {
+ enable = false;
+ mem_profiling_support = false;
+ } else {
+ int res;
+
+ res = kstrtobool(str, &enable);
+ if (res)
+ return res;
+
+ mem_profiling_support = true;
+ }
+
+ if (enable != static_key_enabled(&mem_alloc_profiling_key)) {
+ if (enable)
+ static_branch_enable(&mem_alloc_profiling_key);
+ else
+ static_branch_disable(&mem_alloc_profiling_key);
+ }
+
+ return 0;
+}
+early_param("sysctl.vm.mem_profiling", setup_early_mem_profiling);
+
static __init bool need_page_alloc_tagging(void)
{
- return true;
+ return mem_profiling_support;
}

static __init void init_page_alloc_tagging(void)
@@ -158,6 +195,8 @@ static int __init alloc_tag_init(void)
if (IS_ERR_OR_NULL(alloc_tag_cttype))
return PTR_ERR(alloc_tag_cttype);

+ if (!mem_profiling_support)
+ memory_allocation_profiling_sysctls[0].mode = 0444;
register_sysctl_init("vm", memory_allocation_profiling_sysctls);
procfs_init();

--
2.44.0.291.gc1ea87d7ee-goog