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    SubjectRe: Avoid allocating during interleave from almost full nodes
    On Thu, 30 Nov 2006 23:51:17 -0800
    Paul Jackson <pj@sgi.com> wrote:

    > A month ago, Christoph replied to pj:
    > >
    > > On Sat, 4 Nov 2006, Paul Jackson wrote:
    > >
    > > > Do you know of any existing counters that we could use like this?
    > > >
    > > > Adding a system wide count of pages allocated or scanned, just for
    > > > these fullnode hint caches, bothers me.
    > >
    > > There are already such counters. PGALLOC_* and PGSCAN_*. See
    > > include/linux/vmstat.h
    >
    > These counters depend on CONFIG_VM_EVENT_COUNTERS.
    >
    > The Kconfig comment for CONFIG_VM_EVENT_COUNTERS states:
    >
    > VM event counters are only needed to for event counts to be
    > shown. They have no function for the kernel itself. This
    > option allows the disabling of the VM event counters.
    > /proc/vmstat will only show page counts.
    >
    > (By the way - note the "needed to for event" phrasing error.)
    >
    > The header file, include/linux/vmstat.h, for these counters states:
    >
    > /*
    > * Light weight per cpu counter implementation.
    > *
    > * Counters should only be incremented and no critical kernel component
    > * should rely on the counter values.
    >
    > Both these clearly state that I should not use these counters for real
    > kernel functions.
    >
    > If that is so, I should find some other "time base" for the zonelist
    > caching.
    >
    > If that is not so, then these comments need updating.
    >
    > Anybody have any idea which is the case?

    You need to set EMBEDDED to disable VM_EVENT_COUNTERS.

    Things like procps (vmstat, top, etc) now use /proc/vmstat and would likely
    break.

    I don't know how much space it saves, but I doubt if the world would end if
    we removed CONFIG_VM_EVENT_COUNTERS.

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