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    SubjectRe: [PATCH v6 1/4] mm: add NR_SECONDARY_PAGETABLE to count secondary page table uses.
    On Tue, Jun 28, 2022, Yosry Ahmed wrote:
    > We keep track of several kernel memory stats (total kernel memory, page
    > tables, stack, vmalloc, etc) on multiple levels (global, per-node,
    > per-memcg, etc). These stats give insights to users to how much memory
    > is used by the kernel and for what purposes.
    >
    > Currently, memory used by kvm mmu is not accounted in any of those

    Nit, capitalize KVM (mainly to be consistent).

    > @@ -1085,6 +1086,9 @@ KernelStack
    > Memory consumed by the kernel stacks of all tasks
    > PageTables
    > Memory consumed by userspace page tables
    > +SecPageTables
    > + Memory consumed by secondary page tables, this currently
    > + currently includes KVM mmu allocations on x86 and arm64.

    Nit, this line has a tab instead of eight spaces. Not sure if it actually matters,
    there are plenty of tabs elsewhere in the file, but all the entries in this block
    use only spaces.

    > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
    > index aab70355d64f3..13190d298c986 100644
    > --- a/include/linux/mmzone.h
    > +++ b/include/linux/mmzone.h
    > @@ -216,6 +216,7 @@ enum node_stat_item {
    > NR_KERNEL_SCS_KB, /* measured in KiB */
    > #endif
    > NR_PAGETABLE, /* used for pagetables */
    > + NR_SECONDARY_PAGETABLE, /* secondary pagetables, e.g. kvm shadow pagetables */

    Nit, s/kvm/KVM, and drop the "shadow", which might be misinterpreted as saying KVM
    pagetables are only accounted when KVM is using shadow paging. KVM's usage of "shadow"
    is messy, so I totally understand why you included it, but in this case it's unnecessary
    and potentially confusing.

    And finally, something that's not a nit. Should this be wrapped with CONFIG_KVM
    (using IS_ENABLED() because KVM can be built as a module)? That could be removed
    if another non-KVM secondary MMU user comes along, but until then, #ifdeffery for
    stats the depend on a single feature seems to be the status quo for this code.

    > #ifdef CONFIG_SWAP
    > NR_SWAPCACHE,
    > #endif

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