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tracing: Use xarray for syscall trace events 

Currently, a lot of memory is wasted for architectures like MIPS when
init_ftrace_syscalls() allocates the array for syscalls using kcalloc.
This is because syscalls numbers start from 4000, 5000 or 6000 and
array elements up to that point are unused.
Fix this by using a data structure more suited to storing sparsely
populated arrays. The XARRAY data structure, implemented using radix
trees, is much more memory efficient for storing the syscalls in
question.

Link: http://lkml.kernel.org/r/20191115234314.21599-1-hnaveed@wavecomp.com

Signed-off-by: Hassan Naveed <hnaveed@wavecomp.com>
Reviewed-by: Paul Burton <paulburton@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Hassan Naveed 2019-11-15 23:44:42 +00:00 committed by Steven Rostedt (VMware)
parent 89ed42495e
commit 0e24220821
2 changed files with 32 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/Kconfig
View File

@ -960,6 +960,14 @@ config RELR
config ARCH_HAS_MEM_ENCRYPT
bool
config HAVE_SPARSE_SYSCALL_NR
bool
help
An architecture should select this if its syscall numbering is sparse
to save space. For example, MIPS architecture has a syscall array with
entries at 4000, 5000 and 6000 locations. This option turns on syscall
related optimizations for a given architecture.
source "kernel/gcov/Kconfig"
source "scripts/gcc-plugins/Kconfig"

30
kernel/trace/trace_syscalls.c
View File

@ -7,6 +7,7 @@
#include <linux/module.h> /* for MODULE_NAME_LEN via KSYM_SYMBOL_LEN */
#include <linux/ftrace.h>
#include <linux/perf_event.h>
#include <linux/xarray.h>
#include <asm/syscall.h>
#include "trace_output.h"
@ -30,6 +31,7 @@ syscall_get_enter_fields(struct trace_event_call *call)
extern struct syscall_metadata *__start_syscalls_metadata[];
extern struct syscall_metadata *__stop_syscalls_metadata[];
static DEFINE_XARRAY(syscalls_metadata_sparse);
static struct syscall_metadata **syscalls_metadata;
#ifndef ARCH_HAS_SYSCALL_MATCH_SYM_NAME
@ -101,6 +103,9 @@ find_syscall_meta(unsigned long syscall)
static struct syscall_metadata *syscall_nr_to_meta(int nr)
{
if (IS_ENABLED(CONFIG_HAVE_SPARSE_SYSCALL_NR))
return xa_load(&syscalls_metadata_sparse, (unsigned long)nr);
if (!syscalls_metadata || nr >= NR_syscalls || nr < 0)
return NULL;
@ -536,12 +541,16 @@ void __init init_ftrace_syscalls(void)
struct syscall_metadata *meta;
unsigned long addr;
int i;
void *ret;
syscalls_metadata = kcalloc(NR_syscalls, sizeof(*syscalls_metadata),
GFP_KERNEL);
if (!syscalls_metadata) {
WARN_ON(1);
return;
if (!IS_ENABLED(CONFIG_HAVE_SPARSE_SYSCALL_NR)) {
syscalls_metadata = kcalloc(NR_syscalls,
sizeof(*syscalls_metadata),
GFP_KERNEL);
if (!syscalls_metadata) {
WARN_ON(1);
return;
}
}
for (i = 0; i < NR_syscalls; i++) {
@ -551,7 +560,16 @@ void __init init_ftrace_syscalls(void)
continue;
meta->syscall_nr = i;
syscalls_metadata[i] = meta;
if (!IS_ENABLED(CONFIG_HAVE_SPARSE_SYSCALL_NR)) {
syscalls_metadata[i] = meta;
} else {
ret = xa_store(&syscalls_metadata_sparse, i, meta,
GFP_KERNEL);
WARN(xa_is_err(ret),
"Syscall memory allocation failed\n");
}
}
}