zcache: Set SWIZ_BITS to 8 to reduce tmem bucket lock contention.
SWIZ_BITS > 8 results in a much larger number of "tmem_obj" allocations, likely one per page-placed-in-frontswap. The tmem_obj is not huge (roughly 100 bytes), but it is large enough to add a not-insignificant memory overhead to zcache. The SWIZ_BITS=8 will get roughly the same lock contention without the space wastage. The effect of SWIZ_BITS can be thought of as "2^SWIZ_BITS is the number of unique oids that be generated" (This concept is limited to frontswap's use of tmem). Acked-by: NSeth Jennings <sjenning@linux.vnet.ibm.com> Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: stable <stable@vger.kernel.org> Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
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