memcg: increase the valid index range for memcg stats

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.

Link: https://lkml.kernel.org/r/20240730150158.832783-1-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20240724203322.2765486-1-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20240724203322.2765486-2-pasha.tatashin@soleen.com
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Li Zhijian <lizhijian@fujitsu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>