Linux paging and swapping (2.4.18)

Shaw, Marco (Marco.Shaw@aliant.ca)
Tue, 3 Jun 2003 15:03:51 -0300


(First, my apologies for using a Windows email client which will typically format things badly.)

I've been trying to understand Linux paging. Does anyone have any good online links, some
'hidden treasure' of some kind of presentation on Linux 2.4 MM, or any recent books?

Yes, reading the source is best, but I'm years away from being able to read C proficiently.

My underlying problem is I have a system with daily average 'pages in'/second between 0.02-56.21, and
'pages out'/second between 49.89-66.15 in a summary below. I'm trying to figure out if this is an
issue, and what might be the cause. In the meantime, I'm trying to get a better understanding
of Linux MM at a higher level.

Marco

-----Original Message-----
From: Shaw, Marco
Sent: Thursday, May 29, 2003 2:05 PM
To: 'linux-raid@vger.kernel.org'
Subject: RE: Heavy paging, but no swap being used.--MORE INFO

I was asked what I meant by "heavy page in/page out", and I'll do my best...

We have a monitoring system that believes anything over 10 for pages/second could be a problem, and
20 is really bad.

I've gathered this from one of my systems, where:
Pgs_in=pages_in (average for day)
Pgs_in_max=pags_in_maximum (maximum value for day)
Pgs_out=pages_out (average for day)
Pgs_out_max=pags_out_maximum (maximum value for day)

Some output from one of our Linux systems:
sample_date pgs_in pgs_in_max pgs_out pgs_out_max
5/16/2003 0.07 5.68 53.32 159.54
5/17/2003 0.04 3.27 49.89 167.2
5/18/2003 0.09 5.74 50.57 159.61
5/19/2003 0.02 0.04 51.55 160.07
5/20/2003 25.86 657.06 57.06 166.05
5/21/2003 56.21 970.79 66.15 156.4
5/22/2003 10.48 1371.75 58.27 168.07
5/23/2003 0.33 39.9 56.77 148.58
5/24/2003 0.03 0.26 56.2 162.94
5/25/2003 0.02 0.49 56.45 166.74
5/26/2003 0.05 1.13 65.62 173.82
5/27/2003 36.8 754.51 64 203.06

Hence that difficult question of what is the norm? I'm trying to figure out if I have
a problem Or this is 'normal' for the system: a dual-CPU 1.4GHz PIII with 4GB of RAM.
The OS is on a local Hardware RAID card, but other data/apps are on a SAN attached
software RAID0 device.

Marco

> -----Original Message-----
> From: Shaw, Marco
> Sent: Thursday, May 29, 2003 11:31 AM
> To: 'linux-raid@vger.kernel.org'
> Subject: Heavy paging, but no swap being used.
>
>
> RedHat 7.2 with 2.4.18-18.7.xbigmem using RedHat's software
> RAID package.
>
> I've been seeing quite a bit of page in/page out going on,
> and have been looking around.
>
> With the 2.4 kernel, when would one expect to see swap usage?
> I'm assuming the 2.4 memory works a bit like Solaris where
> one should expect to see physical memory usage relatively
> high, and that's a good/normal thing, but I don't see any
> swap utilization at all, which concerns me. I may have
> misconfigured something...
>
> How can I pin-point, if possible, whether the paging is
> related to the use of software RAID?
>
> Marco
>
> # more raidtab
> raiddev /dev/md0
> raid-level 0
> nr-raid-disks 2
> persistent-superblock 1
> chunk-size 32
> device /dev/sdc1
> raid-disk 0
> device /dev/sdd1
> raid-disk 1
>
> # free
> total used free shared buffers
> cached
> Mem: 3874464 3843256 31208 0
> 381844 3084184
> -/+ buffers/cache: 377228 3497236
> Swap: 2048248 0 2048248
>
> # sar -r
> Linux 2.4.18-18.7.xbigmem 05/29/2003
>
> 12:00:00 AM kbmemfree kbmemused %memused kbmemshrd kbbuffers
> kbcached kbswpfree kbswpused %swpused
> 12:10:00 AM 33956 3840508 99.12 0 381020
> 3085476 2048248 0 0.00
>
> # swapon -s
> Filename Type Size Used
> Priority
> /dev/sda6 partition 2048248 0 -1
>
> # more /etc/fstab
> LABEL=/ / ext3
> defaults 1 1
> LABEL=/boot /boot ext3
> defaults 1 2
> none /dev/pts devpts
> gid=5,mode=620 0 0
> LABEL=/home /home ext3
> defaults 1 2
> none /proc proc
> defaults 0 0
> none /dev/shm tmpfs
> defaults 0 0
> LABEL=/tmp /tmp ext3
> defaults 1 2
> LABEL=/usr /usr ext3
> defaults 1 2
> LABEL=/var /var ext3
> defaults 1 2
> /dev/md0 /hosting ext3 defaults,usrquota 0 0
> /dev/sda6 swap swap
> defaults 0 0
> /dev/cdrom /mnt/cdrom iso9660
> noauto,owner,kudzu,ro 0
> 0
> /dev/fd0 /mnt/floppy auto
> noauto,owner,kudzu 0 0
>
>
> # sar -B
> Linux 2.4.18-18.7.xbigmem 05/29/2003
>
> 12:00:00 AM pgpgin/s pgpgout/s activepg inadtypg inaclnpg
> inatarpg ...
> Average: 0.02 55.34 561672 225090 115799
> 180512
>
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