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    Subject[09/17] VFALLBACK: Debugging aid
    Virtual fallbacks are rare and thus subtle bugs may creep in if we do not
    test the fallbacks. CONFIG_VFALLBACK_ALWAYS makes all GFP_VFALLBACK
    allocations fall back to virtual mapping.

    Signed-off-by: Christoph Lameter <clameter@sgi.com>

    ---
    lib/Kconfig.debug | 11 +++++++++++
    mm/page_alloc.c | 6 ++++++
    2 files changed, 17 insertions(+)

    Index: linux-2.6/mm/page_alloc.c
    ===================================================================
    --- linux-2.6.orig/mm/page_alloc.c 2007-09-24 18:48:03.000000000 -0700
    +++ linux-2.6/mm/page_alloc.c 2007-09-24 18:58:52.000000000 -0700
    @@ -1208,6 +1208,12 @@ zonelist_scan:
    }
    }

    +#ifdef CONFIG_VFALLBACK_ALWAYS
    + if ((gfp_mask & __GFP_VFALLBACK) &&
    + system_state == SYSTEM_RUNNING)
    + return vcompound_alloc(gfp_mask, order,
    + zonelist, alloc_flags);
    +#endif
    page = buffered_rmqueue(zonelist, zone, order, gfp_mask);
    if (page)
    break;
    Index: linux-2.6/lib/Kconfig.debug
    ===================================================================
    --- linux-2.6.orig/lib/Kconfig.debug 2007-09-24 18:30:45.000000000 -0700
    +++ linux-2.6/lib/Kconfig.debug 2007-09-24 18:48:06.000000000 -0700
    @@ -105,6 +105,17 @@ config DETECT_SOFTLOCKUP
    can be detected via the NMI-watchdog, on platforms that
    support it.)

    +config VFALLBACK_ALWAYS
    + bool "Always fall back to Virtual Compound pages"
    + default y
    + help
    + Virtual compound pages are only allocated if there is no linear
    + memory available. They are a fallback and errors created by the
    + use of virtual mappings instead of linear ones may not surface
    + because of their infrequent use. This option makes every
    + allocation that allows a fallback to a virtual mapping use
    + the virtual mapping. May have a significant performance impact.
    +
    config SCHED_DEBUG
    bool "Collect scheduler debugging info"
    depends on DEBUG_KERNEL && PROC_FS
    --
    -
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