Re: [PATCH]: VM 6/8 page_referenced(): move dirty

[Andrew Morton <akpm@osdl.org>]

Nikita Danilov <nikita@clusterfs.com> wrote:
>
> Andrew Morton writes:
>   > Nikita Danilov <nikita@clusterfs.com> wrote:
>   > >
>   > >   > 
>   > >   > I can envision workloads (such as mmap 80% of memory and continuously dirty
>   > >   > it) which would end up performing continuous I/O with this patch.
>   > > 
>   > >  Below is a version that tries to move dirtiness to the struct page only
>   > >  if we are really going to deactivate the page. In your scenario above,
>   > >  continuously dirty pages will be on the active list, so it should be
>   > >  okay.
>   > 
>   > OK, well it'll now increase the amount of I/O by a smaller amount.  Trade
>   > that off against possibly improved I/O patterns.  But how do we know that
>   > all this is a net gain?
> 
>  By looking at the (micro-) benchmarking results:
> 
>  2.6.12-rc2:
> 
>  before-patch page_referenced-move-dirty
> 
>          45.8  32.3
>         204.3  93.2
>         194.8  89.5
>         194.9  89.9
>         197.7  92.1
>         195.0  90.2
>         199.4  89.5
>         196.3  89.2

hm.  What's the reason for such a large difference?  That workload should
just be doing pretty-much-linear write even if we're writing a
page-at-a-time off the tail of the LRU.

Was that box SMP?
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