Re: [RFC 7/7] Switch of PF_MEMALLOC during writeout

[Christoph Lameter]

On Mon, 21 Aug 2007, Andi Kleen wrote:

> Christoph Lameter <clameter@xxxxxxx> writes:
> 
> > Switch off PF_MEMALLOC during both direct and kswapd reclaim.
> > 
> > This works because we are not holding any locks at that point because
> > reclaim is essentially complete. The write occurs when the memory on
> > the zones is at the high water mark so it is unlikely that writeout
> > will get into trouble. If so then reclaim can be called recursively to
> > reclaim more pages.
> 
> What would stop multiple recursions in extreme low memory cases? Seems 
> risky to me and risking stack overflow.  Perhaps define another flag to catch that?

Right. I am not sure exactly how to handle that. There is also the issue 
of the writes being deferred. I thought maybe of using pdflush to writeout 
the pages? Maybe increase priority of the pdflush so that it runs 
immediately when notified. Shrink_page_list would gather the dirty pages 
in pvecs and then forward to a pdflush. That may make the whole thing much 
cleaner.

Opinions?


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