Re: [patch 05/10] slub: Remove slub_nomerge

[Hugh Dickins <hugh@veritas.com>]

On Thu, 28 Feb 2008, Christoph Lameter wrote:
> No one has used that option for a long time and AFAICT its currently utterly
> useless.

Not so at all.  I certainly use it: not often, but from time to time,
in debugging.  If you're narrowing down on something, it's a worthwhile
tool to separate the different uses of a particular size.

And when studying slabinfo numbers, perhaps for a leak e.g. why doesn't
slabinfo doesn't show vm_area_struct, oh, it's sharing :0000088 with
cfq_queue, so we need slub_nomerge to see their actual numbers.
Perhaps I'm missing something: how does everyone else get the
right numbers without slub_nomerge?

Admittedly it's often too blunt an instrument for debugging: I'd be
happier with a debug flag which has no other side-effect than nomerge
(all the other SLUB_NEVER_MERGE flags seemed to have side-effects that
I wanted to avoid when trying to reproduce an elusive corruption),
that can be applied to a single cache as well as to the whole lot.

I could add that if you don't (or I could hack my mm/slub.c when
I need to, that's always an option: but I do think nomerge can be
useful out in the field).  If you go ahead and remove slub_nomerge,
please also remove it from Documentation/kernel-parameters.txt.

Hugh

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