linux-kernel - Re: I have a blaze of 353 page allocation failures, all alike

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Date:	Wed, 13 Apr 2011 09:13:46 +0200
From:	Peter Kruse <pk@...eap.de>
To:	David Rientjes <rientjes@...gle.com>
CC:	Christoph Lameter <cl@...ux.com>, eric.dumazet@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: I have a blaze of 353 page allocation failures, all alike

Hello,

thanks for your replies, I appreciate that.

On 04/13/2011 03:34 AM, David Rientjes wrote:
> On Tue, 12 Apr 2011, Christoph Lameter wrote:
>
>> The problem maybe that you have lots and lots of SCSI devices which
>> consume ZONE_DMA memory for their control structures. I guess that is
>> oversubscribing the 16M zone.

but there are only two devices:

# fdisk -l

Disk /dev/sda: 249.8 GB, 249865175040 bytes
255 heads, 63 sectors/track, 30377 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x4ac39024

    Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          13      104422   83  Linux
/dev/sda2              14       30377   243898830   8e  Linux LVM

WARNING: GPT (GUID Partition Table) detected on '/dev/sdb'! The util fdisk 
doesn't support GPT. Use GNU Parted.


Disk /dev/sdb: 37946.0 GB, 37946025574400 bytes
255 heads, 63 sectors/track, 4613341 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Disk /dev/sdb doesn't contain a valid partition table

> You can try to get more memory reserves specifically for lowmem in
> ZONE_DMA by changing /proc/sys/vm/lowmem_reserve_ratio.  The values are
> ratios, so lowering the numbers will yield larger amounts of memory
> reserves in ZONE_DMA for GFP_DMA allocations.  Try lowering the non-zero
> entries to 1 to reserve the entire zone for lowmem, assuming your system
> has enough RAM for everything else you're running.

this server has 48GB - that should be enough.

> This will verify if ZONE_DMA is being depleted from the larger number of
> SCSI devices.  If you don't get any additional page allocation failures,
> then check how much memory in ZONE_DMA is used at peak and that would be a
> sane reserve ratio to use next time you restart the system.

Could that still be a problem if there are only two scsi devices?

Regards,

   Peter
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