On Mon, 2024-02-12 at 18:09 -0500, Steven Rostedt wrote: > From: "Steven Rostedt (Google)" <rost...@goodmis.org> > > The saved_cmdlines have three arrays for mapping PIDs to COMMs: > > - map_pid_to_cmdline[] > - map_cmdline_to_pid[] > - saved_cmdlines > > The map_pid_to_cmdline[] is PID_MAX_DEFAULT in size and holds the index > into the other arrays. The map_cmdline_to_pid[] is a mapping back to the > full pid as it can be larger than PID_MAX_DEFAULT. And the > saved_cmdlines[] just holds the COMMs associated to the pids. > > Currently the map_pid_to_cmdline[] and saved_cmdlines[] are allocated > together (in reality the saved_cmdlines is just in the memory of the > rounding of the allocation of the structure as it is always allocated in > powers of two). The map_cmdline_to_pid[] array is allocated separately. > > Since the rounding to a power of two is rather large (it allows for 8000 > elements in saved_cmdlines), also include the map_cmdline_to_pid[] array. > (This drops it to 6000 by default, which is still plenty for most use > cases). This saves even more memory as the map_cmdline_to_pid[] array > doesn't need to be allocated.
This patch does make better use of the extra space and make the previous change better. Reviewed-by: Tim Chen <tim.c.c...@linux.intel.com> > > Link: > https://lore.kernel.org/linux-trace-kernel/20240212174011.06821...@gandalf.local.home/ > > Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org> > --- > kernel/trace/trace_sched_switch.c | 13 ++++--------- > 1 file changed, 4 insertions(+), 9 deletions(-) > > diff --git a/kernel/trace/trace_sched_switch.c > b/kernel/trace/trace_sched_switch.c > index e4fbcc3bede5..210c74dcd016 100644 > --- a/kernel/trace/trace_sched_switch.c > +++ b/kernel/trace/trace_sched_switch.c > @@ -201,7 +201,7 @@ static struct saved_cmdlines_buffer > *allocate_cmdlines_buffer(unsigned int val) > int order; > > /* Figure out how much is needed to hold the given number of cmdlines */ > - orig_size = sizeof(*s) + val * TASK_COMM_LEN; > + orig_size = sizeof(*s) + val * (TASK_COMM_LEN + sizeof(int)); Strictly speaking, *map_cmdline_to_pid is unsigned int so it is more consistent to use sizeof(unsigned) in line above. But I'm nitpicking and I'm fine to leave it as is. > order = get_order(orig_size); > size = 1 << (order + PAGE_SHIFT); > page = alloc_pages(GFP_KERNEL, order); > @@ -212,16 +212,11 @@ static struct saved_cmdlines_buffer > *allocate_cmdlines_buffer(unsigned int val) > memset(s, 0, sizeof(*s)); > > /* Round up to actual allocation */ > - val = (size - sizeof(*s)) / TASK_COMM_LEN; > + val = (size - sizeof(*s)) / (TASK_COMM_LEN + sizeof(int)); > s->cmdline_num = val; > > - s->map_cmdline_to_pid = kmalloc_array(val, > - sizeof(*s->map_cmdline_to_pid), > - GFP_KERNEL); > - if (!s->map_cmdline_to_pid) { > - free_saved_cmdlines_buffer(s); > - return NULL; > - } > + /* Place map_cmdline_to_pid array right after saved_cmdlines */ > + s->map_cmdline_to_pid = (unsigned *)&s->saved_cmdlines[val * > TASK_COMM_LEN]; > > s->cmdline_idx = 0; > memset(&s->map_pid_to_cmdline, NO_CMDLINE_MAP,
