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Date: Wed, 10 Jul 2002 18:34:22 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: Lukas Hejtmanek <xhejtman@mail.muni.cz>
Cc: "J.A. Magallon" <jamagallon@able.es>,
       Austin Gonyou <austin@digitalroadkill.net>,
       linux-kernel@vger.kernel.org, linux-scsi@dualathlon.random
Subject: Re: Terrible VM in 2.4.11+ again?
Message-ID: <20020710163422.GB2513@dualathlon.random>
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On Tue, Jul 09, 2002 at 12:48:08PM +0200, Lukas Hejtmanek wrote:
> On Tue, Jul 09, 2002 at 12:58:16AM +0200, J.A. Magallon wrote:
> > Seriously, if you have that kind of problems, take the -aa kernel and use it.
> > I use it regularly and it behaves as one would expect, and fast.
> > And please, report your results...
> 
> I've tried 2.4.19rc1aa2, it swaps even when I have 512MB ram and xcdroast with
> scsi-ide emulation cd writer reports to syslog:
> Jul  9 12:45:02 hell kernel: __alloc_pages: 3-order allocation failed
> (gfp=0x20/0)
> Jul  9 12:45:02 hell kernel: __alloc_pages: 3-order allocation failed
> (gfp=0x20/0)
> Jul  9 12:45:02 hell kernel: __alloc_pages: 2-order allocation failed
> (gfp=0x20/0)
> Jul  9 12:45:02 hell kernel: __alloc_pages: 1-order allocation failed
> (gfp=0x20/0)
> Jul  9 12:45:02 hell kernel: __alloc_pages: 0-order allocation failed
> (gfp=0x20/0)
> 
> Am I something missing?

you may want to reproduce with vm_debug set to 1, but I'm pretty sure
it's a scsi generic issue, they are allocating ram with GFP_ATOMIC, and
they may eventually fail if kswapd cannot keep up with the other
GFP_ATOMIC allocations. They should use GFP_NOIO, with -aa it won't even
try to unmap pages.  It will just try to shrink clean cache and it
should work fine for the above purpose where the allocation needs low
latency (the local_pages per-task ensures their work won't be stolen by
the GFP_ATOMIC users).  I asked for that change some time ago but it
never happened apparently. However I assume the sr layer tried some more
after failing, sg has a quite large queue so some delay isn't fatal, and
you can probably safely ignore the above messages, they're just warnings
for you. nevertheless GFP_NOIO would make the allocations more reliable.

Andrea
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