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+Short users guide for SLUB
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+--------------------------
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+
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+First of all slub should transparently replace SLAB. If you enable
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+SLUB then everything should work the same (Note the word "should".
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+There is likely not much value in that word at this point).
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+
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+The basic philosophy of SLUB is very different from SLAB. SLAB
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+requires rebuilding the kernel to activate debug options for all
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+SLABS. SLUB always includes full debugging but its off by default.
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+SLUB can enable debugging only for selected slabs in order to avoid
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+an impact on overall system performance which may make a bug more
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+difficult to find.
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+
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+In order to switch debugging on one can add a option "slub_debug"
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+to the kernel command line. That will enable full debugging for
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+all slabs.
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+
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+Typically one would then use the "slabinfo" command to get statistical
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+data and perform operation on the slabs. By default slabinfo only lists
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+slabs that have data in them. See "slabinfo -h" for more options when
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+running the command. slabinfo can be compiled with
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+
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+gcc -o slabinfo Documentation/vm/slabinfo.c
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+
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+Some of the modes of operation of slabinfo require that slub debugging
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+be enabled on the command line. F.e. no tracking information will be
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+available without debugging on and validation can only partially
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+be performed if debugging was not switched on.
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+
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+Some more sophisticated uses of slub_debug:
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+-------------------------------------------
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+
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+Parameters may be given to slub_debug. If none is specified then full
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+debugging is enabled. Format:
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+
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+slub_debug=<Debug-Options> Enable options for all slabs
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+slub_debug=<Debug-Options>,<slab name>
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+ Enable options only for select slabs
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+
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+Possible debug options are
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+ F Sanity checks on (enables SLAB_DEBUG_FREE. Sorry
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+ SLAB legacy issues)
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+ Z Red zoning
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+ P Poisoning (object and padding)
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+ U User tracking (free and alloc)
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+ T Trace (please only use on single slabs)
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+
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+F.e. in order to boot just with sanity checks and red zoning one would specify:
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+
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+ slub_debug=FZ
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+
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+Trying to find an issue in the dentry cache? Try
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+
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+ slub_debug=,dentry_cache
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+
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+to only enable debugging on the dentry cache.
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+
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+Red zoning and tracking may realign the slab. We can just apply sanity checks
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+to the dentry cache with
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+
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+ slub_debug=F,dentry_cache
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+
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+In case you forgot to enable debugging on the kernel command line: It is
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+possible to enable debugging manually when the kernel is up. Look at the
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+contents of:
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+
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+/sys/slab/<slab name>/
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+
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+Look at the writable files. Writing 1 to them will enable the
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+corresponding debug option. All options can be set on a slab that does
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+not contain objects. If the slab already contains objects then sanity checks
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+and tracing may only be enabled. The other options may cause the realignment
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+of objects.
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+
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+Careful with tracing: It may spew out lots of information and never stop if
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+used on the wrong slab.
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+
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+SLAB Merging
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+------------
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+
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+If no debugging is specified then SLUB may merge similar slabs together
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+in order to reduce overhead and increase cache hotness of objects.
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+slabinfo -a displays which slabs were merged together.
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+
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+Getting more performance
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+------------------------
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+
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+To some degree SLUB's performance is limited by the need to take the
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+list_lock once in a while to deal with partial slabs. That overhead is
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+governed by the order of the allocation for each slab. The allocations
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+can be influenced by kernel parameters:
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+
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+slub_min_objects=x (default 8)
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+slub_min_order=x (default 0)
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+slub_max_order=x (default 4)
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+
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+slub_min_objects allows to specify how many objects must at least fit
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+into one slab in order for the allocation order to be acceptable.
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+In general slub will be able to perform this number of allocations
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+on a slab without consulting centralized resources (list_lock) where
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+contention may occur.
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+
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+slub_min_order specifies a minim order of slabs. A similar effect like
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+slub_min_objects.
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+
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+slub_max_order specified the order at which slub_min_objects should no
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+longer be checked. This is useful to avoid SLUB trying to generate
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+super large order pages to fit slub_min_objects of a slab cache with
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+large object sizes into one high order page.
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+
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+
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+Christoph Lameter, <clameter@sgi.com>, April 10, 2007
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Christoph Lameter