On Fri, Feb 25, 2022 at 07:03:18PM +0100, Vlastimil Babka wrote:
> From: Oliver Glitta <glittao@xxxxxxxxx>
>
> Add description of debugfs files alloc_traces and free_traces
> to SLUB cache documentation.
>
> [ vbabka@xxxxxxx: some rewording ]
>
> Signed-off-by: Oliver Glitta <glittao@xxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> ---
> Documentation/vm/slub.rst | 61 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 61 insertions(+)
>
> diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
> index d3028554b1e9..2b2b931e59fc 100644
> --- a/Documentation/vm/slub.rst
> +++ b/Documentation/vm/slub.rst
> @@ -384,5 +384,66 @@ c) Execute ``slabinfo-gnuplot.sh`` in '-t' mode, passing all of the
> 40,60`` range will plot only samples collected between 40th and
> 60th seconds).
>
> +
> +DebugFS files for SLUB
> +======================
> +
> +For more information about current state of SLUB caches with the user tracking
> +debug option enabled, debugfs files are available, typically under
> +/sys/kernel/debug/slab/<cache>/ (created only for caches with enabled user
> +tracking). There are 2 types of these files with the following debug
> +information:
> +
> +1. alloc_traces::
> +
> + Prints information about unique allocation traces of the currently
> + allocated objects. The output is sorted by frequency of each trace.
> +
> + Information in the output:
> + Number of objects, allocating function, minimal/average/maximal jiffies since alloc,
> + pid range of the allocating processes, cpu mask of allocating cpus, and stack trace.
> +
> + Example:::
> +
> + 1085 populate_error_injection_list+0x97/0x110 age=166678/166680/166682 pid=1 cpus=1::
> + __slab_alloc+0x6d/0x90
> + kmem_cache_alloc_trace+0x2eb/0x300
> + populate_error_injection_list+0x97/0x110
> + init_error_injection+0x1b/0x71
> + do_one_initcall+0x5f/0x2d0
> + kernel_init_freeable+0x26f/0x2d7
> + kernel_init+0xe/0x118
> + ret_from_fork+0x22/0x30
> +
> +
> +2. free_traces::
> +
> + Prints information about unique free traces of the currently free objects,
> + sorted by their frequency.
> +
I'm not sure that it's traces of the "currently free objects".
static int slab_debug_trace_open(struct inode *inode, struct file *filep)
{
[...]
obj_map = bitmap_alloc(oo_objects(s->oo), GFP_KERNEL);
[...]
for_each_kmem_cache_node(s, node, n) {
unsigned long flags;
struct slab *slab;
if (!atomic_long_read(&n->nr_slabs))
continue;
spin_lock_irqsave(&n->list_lock, flags);
list_for_each_entry(slab, &n->partial, slab_list)
process_slab(t, s, slab, alloc, obj_map);
list_for_each_entry(slab, &n->full, slab_list)
process_slab(t, s, slab, alloc, obj_map);
spin_unlock_irqrestore(&n->list_lock, flags);
}
[...]
}
static void __fill_map(unsigned long *obj_map, struct kmem_cache *s,
struct slab *slab)
{
void *addr = slab_address(slab);
void *p;
bitmap_zero(obj_map, slab->objects);
for (p = slab->freelist; p; p = get_freepointer(s, p))
set_bit(__obj_to_index(s, addr, p), obj_map);
}
static void process_slab(struct loc_track *t, struct kmem_cache *s,
struct slab *slab, enum track_item alloc,
unsigned long *obj_map)
{
void *addr = slab_address(slab);
void *p;
__fill_map(obj_map, s, slab);
for_each_object(p, s, addr, slab->objects)
if (!test_bit(__obj_to_index(s, addr, p), obj_map))
add_location(t, s, get_track(s, p, alloc));
}
I think it's not traces of "currently free objects"
because index bit of free objects are set in obj_map bitmap?
It's weird but it's traces of allocated objects that have been freed at
least once (or <not available>)
I think we can fix the code or doc?
Please tell me if I'm missing something :)
> + Information in the output:
> + Number of objects, freeing function, minimal/average/maximal jiffies since free,
> + pid range of the freeing processes, cpu mask of freeing cpus, and stack trace.
> +
> + Example:::
> +
> + 51 acpi_ut_update_ref_count+0x6a6/0x782 age=236886/237027/237772 pid=1 cpus=1
> + kfree+0x2db/0x420
> + acpi_ut_update_ref_count+0x6a6/0x782
> + acpi_ut_update_object_reference+0x1ad/0x234
> + acpi_ut_remove_reference+0x7d/0x84
> + acpi_rs_get_prt_method_data+0x97/0xd6
> + acpi_get_irq_routing_table+0x82/0xc4
> + acpi_pci_irq_find_prt_entry+0x8e/0x2e0
> + acpi_pci_irq_lookup+0x3a/0x1e0
> + acpi_pci_irq_enable+0x77/0x240
> + pcibios_enable_device+0x39/0x40
> + do_pci_enable_device.part.0+0x5d/0xe0
> + pci_enable_device_flags+0xfc/0x120
> + pci_enable_device+0x13/0x20
> + virtio_pci_probe+0x9e/0x170
> + local_pci_probe+0x48/0x80
> + pci_device_probe+0x105/0x1c0
> +
Everything else looks nice!
> Christoph Lameter, May 30, 2007
> Sergey Senozhatsky, October 23, 2015
> --
> 2.35.1
>
>
--
Thank you, You are awesome!
Hyeonggon :-)
