Re: nonblocking-vm.patch

[Andrew Morton <akpm@zip.com.au>]

Rik van Riel wrote:
> 
> ...
> Page_launder (shrink_cache) scans the inactive_dirty list.
> 
> Pages which are ready to be reclaimed get moved to the inactive_clean
> list, from where __alloc_pages() deals with them.
> 

The clang you heard was a penny.  (Nickel?  Dime?)

So you have kswapd running page_launder most of the time, but under
stress, page allocators will do it too.

With all this infrastructure, we can tell beforehand whether
a writeout will block.  And I think that changes everything.  It
presumably means that we can get quite a bit smarter in there - if
kswapd sees a non-blockingly-writeable mapping, go write it and move
the pages <here>.  If kswapd sees some dirty pages which might cause
request queue blockage, then move them <there>.  If the caller is _not_
kswapd then blocking is sometimes desirable, so do something else.

I think I'm pretty much finished mangling vmscan.c (honest).  Let
me get the current stuff settled in and working not-completely-terribly,
then you can get it working properly, OK?  Should be a few days more..

I'll leave the additional instrumentation in place for the while, find some
way of getting the kernel to spit it out on demand.
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