Swap partitions - activation and situation

Hola all dudes,
what the hell is swap partition? It is a sort of virtual memory. If your system have a limited amount of physical memory (in MS4x0H it is 250MB) and some application want's to allocate some more resources, the system will signal the application insufficient amount of free memory to be allocated and application will stops. You can avoid this by adding the physical memory (not possible in MS4x0H situation) or add the virtual memory - it is a space allocated on disk to be used as memory (it can be a full partition or file in filesystem). The partition (or file in filesystem) is called as swap and is added to system with lowest priority and is used as last option to allocate memory.
In Harmony from first version, there is automatic swap partition activation.

I try to describe the swap situation:
The main HDD (internal, for 400H in external bay) is repartitioned as following schema:
1. partition - main partition for all the movies/photos/music and recordings - rest of HDD if you subtract next 3 partitions
2. partition - swap partition - 160MB
3. partition - Linux EXT3 partition for time-shift - size depend of your choice in settings while HDD formating
4. partition - service partition - 160MB

I have following situation while using 1.5TB disk

Código:

root@Venus:~# fdisk -l /dev/sda
Disk /dev/sda: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

  Device Boot      Start        End      Blocks  Id System
/dev/sda1              2      180249  1447842060  7 HPFS/NTFS
/dev/sda2          180250      180269      160650  82 Linux swap
/dev/sda3          180270      182361    16803990  83 Linux
/dev/sda4          182362      182381      160650  83 Linux

The activated swaps can be see in /proc/swaps

Código:

root@Venus:~# cat /proc/swaps
Filename                                Type            Size    Used    Priority
/mnt/rd/swap.img                        file            32      0      -1
/dev/scsi/host1/bus0/target0/lun0/part2 partition      160640  0      -2

Why is this...
The "/mnt/rd/swap.img" is from the original firmware specification. The size is 40kb. This swap MUST BE activated and must be activated as first swap. If you don't do this, the system will not start and constantly reboots.

The second swap is activated from Harmony start. I detect the creation of swap partition but in start scripts there were no activation of this swap. So it is added to startup script of Harmony.
There are some confusing behavior of system:
- if you boot with no USB connected, the HDD is detected as /dev/sda - so all the partitions are seen as /dev/hda1-4
- if you plug any of the USB disk and then turns the PVR on, this USB is detected before the HDD so it takes the /dev/hda and the HDD takes /dev/hdb (I didn't try to connect more than 1 USB disk so there is a possibility if you connect 2 USB disks, the one USB disk takes /dev/hda, he second takes /dev/hdb and HDD takes /dev/hdc) - this is for MS400H with one HDD in bay. If someone can test it for MS450H with installed internal HDD w/wo external HDD, I can supply it.

Best accessing the concrete disk is point to the physical connection - as you can see in list of swaps - "/dev/scsi/host1/bus0/target0/lun0/part2". This is the notation of absolute partition. If we boot without any USB disk the targets are as follows:

Código:

/dev/sda1 = /dev/scsi/host1/bus0/target0/lun0/part1
/dev/sda2 = /dev/scsi/host1/bus0/target0/lun0/part2
/dev/sda3 = /dev/scsi/host1/bus0/target0/lun0/part3
/dev/sda4 = /dev/scsi/host1/bus0/target0/lun0/part4

If you connect the the USB disk, the /dev/sd* devices are changed but /dev/scsi/host1/... devices are still same across all the time.

Why I write this... if you use original firmware, there is only added the 50kB file /mnt/rd/swap.img and the next swap partition on HDD not. So I tell there is no reason to activate this partition for us. It is done by "starthddscript.sh" which is started in boot sequence and after the disk is detected. It will add additional 160MB of virtual memory. So we can see following output of free memory:

Código:

root@Venus:~# free
            total        used        free      shared      buffers
Mem:        250728      246972        3756            0        29888
-/+ buffers:            217084        33644
Swap:      160672            0      160672

So in Harmony we have 400MB of memory.

Hi Keltek,
I disagree with your point:

Keltek escribió:[...]if you use original firmware, there is only added the 50kB file /mnt/rd/swap.img and the next swap partition on HDD not.[...]

I am now running the official firmware MS400_101027_0128.img and this is what I see:

Código:

lg#> cat /proc/swaps
Filename                                Type            Size    Used    Priority
/mnt/rd/swap.img                        file            32      0      -1
/dev/scsi/host0/bus0/target0/lun0/part2 partition    160640      0      -2

cat /proc/meminfo
MemTotal: 250728 kB
MemFree:  128508 kB
Buffers:  13988 kB
[...]
SwapTotal: 160672 kB
SwapFree:  160672 kB
[...]


I don't know how/where it is activated (not in rcS...), but it is actuallt there. Moreover, you can swapoff and swapon it at will (and of course, it correspondingly disapears and appears at /proc/swaps and /proc/meminfo).

Nevertheless, I must say that using official firmware I have never ever seen (I keep a log of the output of free every 5 minutes) more than a few Kbyts (<<32) of used swap.

Best,

Thank you. I used official firmware loong time ago so I only takes what is in boot scripts.
I always forgot the DvdPlayer application which rules them all - there are swapon lines so the "part2" is added by DvdPlayer.

Hi,
I have just made an interesting (I think) test with strictly official firmware MS400_101027_0128.img. After booting the LG and loging in through telnet (while my wife was watching the TV and/or recorded videos in the LG ;)), I have completely deactivated the swap:

Código:

lg#> swapoff /dev/scsi/host0/bus0/target0/lun0/part2
lg#> swapoff /mnt/rd/swap.img                     
lg#> echo 0 > /proc/sys/vm/swappiness
lg#>
lg#> grep -e Mem -e Swap /proc/meminfo
MemTotal: 250728 kB
MemFree: 134560 kB
SwapCached: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB

Then I've gone on doing busyness as usual: watching TV, playing recorded video, doing small tests through the wireless telnet connection, transferring small files through a LG samba-mounted PC directory, etc. As (I) expected, the LG has not cared at all and it has continued working perfectly. -- IMPORTANT EDIT: After systematic testing, this appears not to be true. Some things do work, but others immediately hung the LG.

Then I started a memory-hog process: busybox gzip:

Código:

lg#> cd /tmp/hdd/volumes/HDD1/tmp/
lg#> ~/busybox gzip -c custom.tar  > custom.tar.gz

From previous attempts to gzip this relatively large file, I know that the LG is not powerful enough to completely accomplish this task and the process ends up eating all the available memory, plus the swap if it is available. But now I don't have any swap; so something must finally die ;) After 10 or 15 minutes, I read:

Código:

grep Mem /proc/meminfo
MemTotal: 250728 kB
MemFree:  30356 kB

A few minutes (or seconds) later, I see the free memory under 30000 KB and immediately I hear my wife screaming -- DvdPlayer is hung: not responding to IR commands, not even to the power button. From my telnet sessions, everything was going on O.K. and a few minutes later, according to ps, DvdPlayer was gone (and the TV screen blank, even without the sync signal).

I've killed the busybox gzip when the free memory was about 25000 KB. Then, after issuing a reboot command, everything is now working back again as usual.

Main lessons learned:

1. The LG can work perfectly without swap -- IMPORTANT EDIT: This is not totally true.
2. DvdPlayer starts dying when other application(s) eat memory and bring it under 30000 KB.
3. Exhausting the memory kills the bigest process, but doesn't harm other, smaller processes.
4. Without swap, the LG may hang or fall down when doing these barbarian practices, but flash is not damaged and, after reboot, everything goes on O.K as usual.

Keltec, Victor (and/or anybody else), ¿can you please try to completely deactivate the swap (as in the first three code lines above) and see what happens with the Harmony firmware (PM + Custom)?

Best,

Very very interesting...
this swap /mnt/rd/swap.img must be activated while booting (without it the DvdPlayer won't start) so the deactivating must be after the DvdPlayer is started.
If we disable the swap and keep all the stuff running (lighttp, samba, transmission) the memory will be exhausted faster. For now I don't know the mechanisms of killing the memory intensive processes by kernel, but I think there must be something like white/black list of processes to be or not to be killed.

Keltek escribió:[...]this swap /mnt/rd/swap.img must be activated while booting (without it the DvdPlayer won't start) so the deactivating must be after the DvdPlayer is started.

Yes.

If we disable the swap and keep all the stuff running (lighttp, samba, transmission) the memory will be exhausted faster. For now I don't know the mechanisms of killing the memory intensive processes by kernel, but I think there must be something like white/black list of processes to be or not to be killed.

"OOM killer" is your friend See, for instance:

http://linux-mm.org/OOM_Killer
http://lwn.net/Articles/317814/

and maybe this one too:

http://ubuntuforums.org/showthread.php?t=1524536

Best,

evr escribió:[...]I have completely deactivated the swap: [...] Then I've gone on doing busyness as usual: watching TV, playing recorded video, [...] As (I) expected, the LG has not cared at all and it has continued working perfectly. [...] Main lessons learned: 1. The LG can work perfectly without swap [...]

After more systematic tests, this does not seem to be true, sorry about that. See here for more details.

I will edit the original post.

Best,