On Tue, 11 Sep 2007, Nick Piggin wrote:
> > No you have not explained why the theoretical issues continue to exist
> > given even just considering Lumpy Reclaim in .23 nor what effect the
> > antifrag patchset would have.
>
> So how does lumpy reclaim, your slab patches, or anti-frag have
> much effect on the worst case situation? Or help much against a
> targetted fragmentation attack?
F.e. Lumpy reclaim reclaim neighboring pages and thus works against
fragmentation. So your formulae no longer works.
> > And you have used a 2M pagesize which is
> > irrelevant to this patchset that deals with blocksizes up to 64k. In my
> > experience the use of blocksize < PAGE_COSTLY_ORDER (32k) is reasonably
> > safe.
>
> I used EXACTLY the page sizes that you brought up in your patch
> description (ie. 64K and 2MB).
The patch currently only supports 64k. There is hope that it will support
2M at some point and as mentioned also a special large page pool facility
may be required.
Quoting from the post:
I would like to increase the supported blocksize to very large pages in
the future so that device drives will be capable of providing large
contiguous mapping. For that purpose I think that we need a mechanism to
reserve pools of varying large sizes at boot time. Such a mechanism can
also be used to compensate in situations where one wants to use larger
buffers but defragmentation support is not (yet?) capable to reliably
provide pages of the desired sizes.
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