linux-imx

.. _slub:

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Short users guide for SLUB

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The basic philosophy of SLUB is very different from SLAB. SLAB

requires rebuilding the kernel to activate debug options for all

slab caches. SLUB always includes full debugging but it is off by default.

SLUB can enable debugging only for selected slabs in order to avoid

an impact on overall system performance which may make a bug more

difficult to find.

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In order to switch debugging on one can add an option ``slub_debug``

to the kernel command line. That will enable full debugging for

all slabs.

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Typically one would then use the ``slabinfo`` command to get statistical

data and perform operation on the slabs. By default ``slabinfo`` only lists

slabs that have data in them. See "slabinfo -h" for more options when

running the command. ``slabinfo`` can be compiled with

::

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    gcc -o slabinfo tools/vm/slabinfo.c

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Some of the modes of operation of ``slabinfo`` require that slub debugging

be enabled on the command line. F.e. no tracking information will be

available without debugging on and validation can only partially

be performed if debugging was not switched on.

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Some more sophisticated uses of slub_debug:

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Parameters may be given to ``slub_debug``. If none is specified then full

debugging is enabled. Format:

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slub_debug=<Debug-Options>

    Enable options for all slabs

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slub_debug=<Debug-Options>,<slab name1>,<slab name2>,...

    Enable options only for select slabs (no spaces

    after a comma)

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Possible debug options are::

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    F       Sanity checks on (enables SLAB_DEBUG_CONSISTENCY_CHECKS

            Sorry SLAB legacy issues)

    Z       Red zoning

    P       Poisoning (object and padding)

    U       User tracking (free and alloc)

    T       Trace (please only use on single slabs)

    A       Toggle failslab filter mark for the cache

    O       Switch debugging off for caches that would have

            caused higher minimum slab orders

    -       Switch all debugging off (useful if the kernel is

            configured with CONFIG_SLUB_DEBUG_ON)

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F.e. in order to boot just with sanity checks and red zoning one would specify::

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    slub_debug=FZ

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Trying to find an issue in the dentry cache? Try::

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