memcg: increase the valid index range for memcg stats

Patch series "Kernel stack usage histogram", v6.

Provide histogram of stack sizes for the exited threads:
Example outputs:
Intel:
$ grep kstack /proc/vmstat
kstack_1k 3
kstack_2k 188
kstack_4k 11391
kstack_8k 243
kstack_16k 0

ARM with 64K page_size:
$ grep kstack /proc/vmstat
kstack_1k 1
kstack_2k 340
kstack_4k 25212
kstack_8k 1659
kstack_16k 0
kstack_32k 0
kstack_64k 0


This patch (of 3):

At the moment the valid index for the indirection tables for memcg stats
and events is < S8_MAX.  These indirection tables are used in performance
critical codepaths.  With the latest addition to the vm_events, the
NR_VM_EVENT_ITEMS has gone over S8_MAX.  One way to resolve is to increase
the entry size of the indirection table from int8_t to int16_t but this
will increase the potential number of cachelines needed to access the
indirection table.

This patch took a different approach and make the valid index < U8_MAX. 
In this way the size of the indirection tables will remain same and we
only need to invalid index check from less than 0 to equal to U8_MAX.  In
this approach we have also removed a subtraction from the performance
critical codepaths.

[[email protected]: v6]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Shakeel Butt <[email protected]>
Co-developed-by: Pasha Tatashin <[email protected]>
Signed-off-by: Pasha Tatashin <[email protected]>
Cc: Domenico Cerasuolo <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Li Zhijian <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions