slab, documentation: add description of debugfs files for SLUB caches

Add description of debugfs files alloc_traces and free_traces
to SLUB cache documentation.

[ vbabka@suse.cz: some rewording ]

Signed-off-by: Oliver Glitta <glittao@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-doc@vger.kernel.org
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>

diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
index d3028554b1e9c5e0ec3daffb02696cbae9600b84..43063ade737af246b0dd13b9f0f9fb567cff479b 100644 (file)
--- a/Documentation/vm/slub.rst
+++ b/Documentation/vm/slub.rst
@@ -384,5 +384,69 @@ 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 freeing traces of the currently allocated
+    objects. The freeing traces thus come from the previous life-cycle of the
+    objects and are reported as not available for objects allocated for the first
+    time. The output is sorted by frequency of each trace.
+
+    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:::
+
+    1980 <not-available> age=4294912290 pid=0 cpus=0
+    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
+
 Christoph Lameter, May 30, 2007
 Sergey Senozhatsky, October 23, 2015