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

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Date:	Tue, 11 Sep 2007 22:54:29 +0100
From:	mel@...net.ie (Mel Gorman)
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, 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 (11/09/07 14:48), Christoph Lameter didst pronounce:
> 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.
> 

Warnings == #2 citizen in my mind with known potential failure cases. That
was the point I thought.

> > 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.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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