Re: [PATCH 06/14] Export fragmentation index via/proc/extfrag_index

From: Andrew Morton
Date: Tue Apr 06 2010 - 20:06:36 EST

On Fri, 2 Apr 2010 17:02:40 +0100
Mel Gorman <mel@xxxxxxxxx> wrote:

> Fragmentation index is a value that makes sense when an allocation of a
> given size would fail. The index indicates whether an allocation failure is
> due to a lack of memory (values towards 0) or due to external fragmentation
> (value towards 1). For the most part, the huge page size will be the size
> of interest but not necessarily so it is exported on a per-order and per-zone
> basis via /proc/extfrag_index


Like unusable_index, this seems awfully specialised. Perhaps we could
hide it under CONFIG_MEL, or even put it in debugfs with the intention
of removing it in 6 or 12 months time. Either way, it's hard to
justify permanently adding this stuff to every kernel in the world?

I have a suspicion that all the info in unusable_index and
extfrag_index could be computed from userspace using /proc/kpageflags
(and perhaps a bit of dmesg-diddling to find the zones). If that can't
be done today, I bet it'd be pretty easy to arrange for it.

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