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Date: Thu, 15 Mar 2001 21:56:07 -0300 (BRT)
From: Marcelo Tosatti <marcelo@conectiva.com.br>
To: Ingo Molnar <mingo@elte.hu>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: Reserved memory for highmem bouncing (fwd)
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Ingo, 

Any comments? 

---------- Forwarded message ----------
Date: Wed, 28 Feb 2001 02:02:16 -0300 (BRT)
From: Marcelo Tosatti <marcelo@conectiva.com.br>
To: Ingo Molnar <mingo@elte.hu>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: Reserved memory for highmem bouncing  


Hi Ingo,

I have a question about the highmem page IO deadlock fix which is in
2.4.2-ac. (the emergency memory thing)

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 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.



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