Question about ever growing swap space on raspi 4 4 GB

On a sunny day (Mon, 27 Jan 2020 20:01:23 +0000) it happened druck wrote in :
OK, thnak you. Better avoid it getting full! Seems OK now:
Fri 24 Jan 2020 03:10:42 PM CET: MiB Mem : 3906.0 total, 2891.6 free, 378.2 used, 636.2 buff/cache MiB Swap: 100.0 total, 20.4 free, 79.6 used. 3378.8 avail Mem
Sat 25 Jan 2020 06:46:05 AM CET MiB Mem : 3906.0 total, 2653.7 free, 372.0 used, 880.4 buff/cache MiB Swap: 100.0 total, 24.7 free, 75.3 used. 3380.4 avail Mem
Sun 26 Jan 2020 07:32:08 AM CET MiB Mem : 3906.0 total, 3265.9 free, 370.6 used, 269.5 buff/cache MiB Swap: 100.0 total, 26.9 free, 73.1 used. 3383.9 avail Mem
Mon 27 Jan 2020 07:01:17 AM CET MiB Mem : 3906.0 total, 3364.9 free, 372.7 used, 168.4 buff/cache MiB Swap: 100.0 total, 28.7 free, 71.3 used. 3382.6 avail Mem
Tue 28 Jan 2020 04:40:45 AM CET iB Mem : 3906.0 total, 2881.9 free, 374.7 used, 649.5 buff/cache MiB Swap: 100.0 total, 29.5 free, 70.5 used. 3375.7 avail Mem
Getting better!
So I will leave it running this way, Do not fix it if it works!
For the other poster, as the system is just writing video to disk using a shorter cache (by writing it more often to harddisk) has no bad side affects, the stuff will have to be written to disk anyways. In fact the writing periods will be more often and shorter, but it is the same amount of data, Writing to disk more often causes less long interrupts and keeps more memory available.
In fact Linux caching results in a high video delay on some of my systems (PCs)! 20 seconds for mcamip is normal!
Also it is a security risk, in case of a power failure you lose the last (likely most important part where you see the bad guy cutting the cables) 20 seconds.
Reply to
Jan Panteltje
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thats a serious error
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Reply to
The Natural Philosopher
Nope malloc succeeds and processes get a SEGV when they try to map memory that can't be found.
That is the designed response to out of memory conditions on every flavour of unix I know, what else would you suggest ?
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Steve O'Hara-Smith                          |   Directable Mirror Arrays 
C:\>WIN                                     | A better way to focus the sun 
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Reply to
Ahem A Rivet's Shot
I wouldn't. I am not saying the behaviour is wrong or inappropriate, just that it is in fact always pretty *serious*.
It is te last ditch attempt to prevent a system crashing altogether: and in most cases a hard reboot is a pragmatic option.
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Reply to
The Natural Philosopher
Look at /etc/dphys-swapfile and man dphys-swapfile AFAIK it checks the swap file on startup. Not there => create; already there => check if size as requested.
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Chris Elvidge, England
Reply to
Chris Elvidge
Fair enough, it is of course.
Yep.
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Steve O'Hara-Smith                          |   Directable Mirror Arrays 
C:\>WIN                                     | A better way to focus the sun 
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Reply to
Ahem A Rivet's Shot
Not on all systems: neither the manpage nor /etc/dphys-swapfile exist on this Fedora system - but maybe thats because it has a swap partition.
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Reply to
Martin Gregorie
dphys-swapfile (as I said earlier) is a Raspbian (Debian/Ubuntu) artifact. I can't see why it should exist on Fedora (RedHat?).
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Chris Elvidge, England
Reply to
Chris Elvidge
And it usually kills a process that is the last one you'd choose yourself ...
Reply to
Andy Burns
Not a huge problem as it tends to be pretty random reads and writes of page sized data. It wouldn't make much difference even with a swap partition, which would be a single continuous area.
That is the big problem with swap on flash, but its the pattern of random accesses rather than fragmentation of the file which gives such bad performance.
---druck
Reply to
druck
I missed the 'Debian-only' notice - sorry 'bout that.
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Reply to
Martin Gregorie
A prime example of Sod's Law.
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Steve O'Hara-Smith                          |   Directable Mirror Arrays 
C:\>WIN                                     | A better way to focus the sun 
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Reply to
Ahem A Rivet's Shot
Why is it that when something is lost its always in the last place you look?
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Reply to
The Natural Philosopher
Because you stop looking when you find it of course.
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Steve O'Hara-Smith                          |   Directable Mirror Arrays 
C:\>WIN                                     | A better way to focus the sun 
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Reply to
Ahem A Rivet's Shot
The question that nobody ever asks is:
"Why did yo start looking in the wrong place?".
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Reply to
Martin Gregorie
Leading question. The real question is 'why wasn't it IN the right place?
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Reply to
The Natural Philosopher
...probably both questions have the same answer.
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Reply to
Martin Gregorie
;-)
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Reply to
Michael J. Mahon
I got me a 4B 4Gig, and bought me tiny 128 Gig USB plug, stuck it into the back, configured sufficient Swap space on it and added it to fstab.
Was going to hook one of my 1T SSD USB-3 drives in but when I compiled a reasonably large program with make -j4 I noticed it didn't even use any swap space at all :-)-O so I'll probably just leave the plug in.
el
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Reply to
Dr Eberhard Lisse
I had one of those, and tried it in the Pi, but it got alarmingly hot when in use. Instead I use a Samsung USB 3.1 bar drive, which is larger and made of metal, so dissipates any heat very quickly.
---druck
Reply to
druck

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