Commit 0e242208 authored by Hassan Naveed's avatar Hassan Naveed Committed by Steven Rostedt (VMware)
Browse files

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: default avatarHassan Naveed <hnaveed@wavecomp.com>
Reviewed-by: default avatarPaul Burton <paulburton@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 89ed4249

arch/Kconfig

+8 −0
Original line number Diff line number Diff line
@@ -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"

kernel/trace/trace_syscalls.c

+25 −7
Original line number Diff line number Diff line
@@ -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;
@@ -536,13 +541,17 @@ 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),

	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++) {

		addr = arch_syscall_addr(i);
@@ -551,7 +560,16 @@ void __init init_ftrace_syscalls(void) 
			continue;



		meta->syscall_nr = i;



		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");

		}



	}

}

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