Re: 4g/4g for 2.6.6

[Andrew Morton]

Rik van Riel <riel@xxxxxxxxxx> wrote:
>
> On Tue, 25 May 2004, Rik van Riel wrote:
> 
> > The point is, people like to run bigger workloads on
> > bigger systems. Otherwise they wouldn't bother buying
> > those bigger systems.
> 
> Btw, you're right about the VMAs.  Looking through customer
> stuff a bit more the more common issues are low memory being
> eaten by dentry / inode cache - which you can't always reclaim
> due to files being open, and don't always _want_ to reclaim
> because that could well be a bigger performance hit than the
> 4:4 split.

I did some testing a year or two back with the normal zone wound down to a
few hundred megs - filesytem benchmarks were *severely* impacted by the
increased turnover rate of fs metadata pagecache and VFS caches.  I forget
the details, but it was "wow".

> The primary impact of the dentry / inode cache using memory
> isn't lowmem exhaustion, btw.  It's lowmem fragmentation.
> 
> Fragmentation causes fork trouble (gone with the 4k stacks)
> and trouble for the network layer and kiobuf allocation,
> which still do need higher order allocations.

I'm suspecting we'll end up needing mempools (or something) of 1- and
2-order pages to support large-frame networking.  I'm surprised there isn't
more pressure to do something about this.  Maybe people are increasing
min_free_kbytes.

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