linux-kernel - Re: [00/41] Large Blocksize Support V7 (adds memmap support)

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Date:	Tue, 11 Sep 2007 16:17:02 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <clameter@....com>
Cc:	Mel Gorman <mel@...net.ie>, andrea@...e.de,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
	William Lee Irwin III <wli@...omorphy.com>,
	David Chinner <dgc@....com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Badari Pulavarty <pbadari@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Fengguang Wu <fengguang.wu@...il.com>,
	swin wang <wangswin@...il.com>, totty.lu@...il.com,
	hugh@...itas.com, joern@...ybastard.org
Subject: Re: [00/41] Large Blocksize Support V7 (adds memmap support)

On Wednesday 12 September 2007 07:48, Christoph Lameter wrote:
> On Tue, 11 Sep 2007, Nick Piggin wrote:
> > But that's not my place to say, and I'm actually not arguing that high
> > order pagecache does not have uses (especially as a practical,
> > shorter-term solution which is unintrusive to filesystems).
> >
> > So no, I don't think I'm really going against the basics of what we
> > agreed in Cambridge. But it sounds like it's still being billed as
> > first-order support right off the bat here.
>
> Well its seems that we have different interpretations of what was agreed
> on. My understanding was that the large blocksize patchset was okay
> provided that I supply an acceptable mmap implementation and put a
> warning in.

Yes. I think we differ on our interpretations of "okay". In my interpretation,
it is not OK to use this patch as a way to solve VM or FS or IO scalability
issues, especially not while the alternative approaches that do _not_ have
these problems have not been adequately compared or argued against.


> > But even so, you can just hold an open fd in order to pin the dentry you
> > want. My attack would go like this: get the page size and allocation
> > group size for the machine, then get the number of dentries required to
> > fill a slab. Then read in that many dentries and pin one of them. Repeat
> > the process. Even if there is other activity on the system, it seems
> > possible that such a thing will cause some headaches after not too long a
> > time. Some sources of pinned memory are going to be better than others
> > for this of course, so yeah maybe pagetables will be a bit easier (I
> > don't know).
>
> Well even without slab targeted reclaim: Mel's antifrag will sort the
> dentries into separate blocks of memory and so isolate the issue.

So even after all this time you do not understand what the fundamental
problem is with anti-frag and yet you are happy to waste both our time
in endless flamewars telling me how wrong I am about it.

Forgive me if I'm starting to be rude, Christoph. This is really irritating.
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