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    SubjectRe: [PATCH v9 05/14] mm: multi-gen LRU: groundwork
    On Mon, Mar 14, 2022 at 6:34 PM Huang, Ying <ying.huang@intel.com> wrote:
    >
    > Yu Zhao <yuzhao@google.com> writes:
    >
    > > On Mon, Mar 14, 2022 at 2:09 AM Huang, Ying <ying.huang@intel.com> wrote:
    > >>
    > >> Hi, Yu,
    > >>
    > >> Yu Zhao <yuzhao@google.com> writes:
    > >> > diff --git a/mm/Kconfig b/mm/Kconfig
    > >> > index 3326ee3903f3..747ab1690bcf 100644
    > >> > --- a/mm/Kconfig
    > >> > +++ b/mm/Kconfig
    > >> > @@ -892,6 +892,16 @@ config ANON_VMA_NAME
    > >> > area from being merged with adjacent virtual memory areas due to the
    > >> > difference in their name.
    > >> >
    > >> > +# the multi-gen LRU {
    > >> > +config LRU_GEN
    > >> > + bool "Multi-Gen LRU"
    > >> > + depends on MMU
    > >> > + # the following options can use up the spare bits in page flags
    > >> > + depends on !MAXSMP && (64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP)
    > >>
    > >> LRU_GEN depends on !MAXSMP. So, What is the maximum NR_CPUS supported
    > >> by LRU_GEN?
    > >
    > > LRU_GEN doesn't really care about NR_CPUS. IOW, it doesn't impose a
    > > max number. The dependency is with NODES_SHIFT selected by MAXSMP:
    > > default "10" if MAXSMP
    > > This combined with LAST_CPUPID_SHIFT can exhaust the spare bits in page flags.
    >
    > From the following code snippets from page-flags-layout.h,
    > LAST_CPUPID_SHIFT is related to NR_CPUS instead of NODES_SHIFT.

    It is. But LAST_CPUPID_NOT_IN_PAGE_FLAGS should always work but
    NODE_NOT_IN_PAGE_FLAGS doesn't.

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