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Date: Fri, 16 Mar 2001 03:58:51 -0300 (BRT)
From: Marcelo Tosatti <marcelo@conectiva.com.br>
To: Ingo Molnar <mingo@elte.hu>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: Re: Reserved memory for highmem bouncing (fwd)
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Ok.

Going to write a patch and send you to test RSN.

On Fri, 16 Mar 2001, Ingo Molnar wrote:

> 
> On Thu, 15 Mar 2001, Marcelo Tosatti wrote:
> 
> > The old create_bounce code used to set PF_MEMALLOC on the task flags
> > and call wakeup_bdflush(1) in case GFP_BUFFER page allocation failed.
> > That was broken because flush_dirty_buffers() could try to flush a
> > buffer pointing to highmem page, which would end up in create_bounce
> > again, but with PF_MEMALLOC.
> >
> > Have you tried to make flush_dirty_buffers() only flush buffers
> > pointing to lowmem pages in case the caller wants it to do so?
> 
> this makes sense too - although an emergency pool of some sort never
> hurts, given that highmem buffers cannot be written out without allocating
> bounce buffers. (this makes them more volatile wrt. resource shortages
> than lowmem buffers.) Also, there is no guarantee that flushing lowmem
> buffers yields any free pages.
> 
> > This way you can call flush_dirty_buffers() with the guarantee you're
> > going to free useful (lowmem) memory. This also throttles high mem
> > writes giving priority to low mem ones.
> 
> yep, i think we should do this in addition to the emergency pool thing, it
> should improve balance.
> 
> 	Ingo
> 

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