Re: nr_async_pages and swapin readahead on -ac series

[Marcelo Tosatti <marcelo@conectiva.com.br>]

On Thu, 8 Mar 2001, Stephen C. Tweedie wrote:

> Hi,
> 
> On Wed, Mar 07, 2001 at 10:57:21PM -0300, Marcelo Tosatti wrote:
> >  
> > On the latest 2.4 -ac series, nr_async_pages is only being used to count
> > swap outs, and not for both swap reads and writes (as Linus tree does).
> 
> Seems fine to me.
> 
> > The problem is that nr_async_pages is used to limit swapin readahead based
> > on the number of on flight swap pages (mm/memory.c::swapin_readahead):
> 
> That's probably a mistake: we don't throttle readahead on normal files
> in this manner.
> 
> Swapin is always synchronous: it happens in response to a task's page
> fault.  As such it is always going to be rate-limited automatically.
> I don't think it's too important to count reads in nr_async_pages, nor
> to throttle readaheads if nr_async_pages is too large.

Its not really throttling. We just _bypass_ the readahead's in case we got
too much. 

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