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megalodon
n00b
Joined: 19 Jun 2021
Posts: 19
Location: Rio de Janeiro, Brazil
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 Posted: Sat Dec 18, 2021 2:46 am Post subject: Debian install using less memory than Gentoo |
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Hi guys,
I very recently installed Gentoo on my new machine and Debian on a VM (KVM/QEMU/Virt-manager). My Gentoo setup has a custom kernel planned to fit my machine and free from any other hardware, packages were compiled for my specific architecture. My debian vm has a generic kernel and generic packages. Both machines have (at that time) a minimal install: No DE, WM, wireless, Bluetooth, sound. Nothing but network connection, sshd and htop.
Gentoo memory usage after boot was around 90 MB (after shaving the kernel, before were around 105 MB), and Debian was 50 MB.
I know 50 MB difference is negligible for the user, and that's not the point here. It`s just for educational purposes, how can a generic Debian install use less memory than a customized, compiled, Gentoo install? Is this result expected? Did I forgot some step when installing Gentoo?
Gentoo:
+ Ryzen 5 5600G
+ MSI B450 Mortar MAX
+ 32GB
Debian:
+ Emulated CPU (Maybe a Xeon, I'll check)
+ 4GB |
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mike155
Advocate
Joined: 17 Sep 2010
Posts: 4438
Location: Frankfurt, Germany
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| Posted: Sat Dec 18, 2021 3:15 am Post subject: |
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How do you measure memory consumption?
Do you clear caches before measuring memory consumption?
Please show us the commands you use. |
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Jaglover
Watchman
Joined: 29 May 2005
Posts: 8291
Location: Saint Amant, Acadiana
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megalodon
n00b
Joined: 19 Jun 2021
Posts: 19
Location: Rio de Janeiro, Brazil
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| Posted: Sat Dec 18, 2021 4:11 am Post subject: |
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| mike155 wrote: | How do you measure memory consumption?
Do you clear caches before measuring memory consumption?
Please show us the commands you use. |
I boot, login and then run htop in both cases. As I used the same simple process I thought was a fair comparison. What command do you suggest to clear cache?
| Jaglover wrote: | | The key word here is "customized", did you start your kernel configuration with 'make allnoconfig'? My box uses 110 MB with OpenBox loaded with some additional programs (conky, audacious, tint2, wbar, feh). |
I used make menuconfig as shown in the handbook. I checked what was suggested and unchecked what I know I'll not use like wireless, bluetooth, most hid support and Intel modules. I'll search about allnoconfig. |
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Arctic5824
n00b
Joined: 04 Dec 2021
Posts: 23
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| Posted: Sun Dec 19, 2021 1:23 am Post subject: |
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| megalodon wrote: | | I boot, login and then run htop in both cases. As I used the same simple process I thought was a fair comparison. What command do you suggest to clear cache? |
I recommend you to check out https://www.linuxatemyram.com/ , it is a great resource for understanding _how_ linux uses the ram on the system
a better way to check would be "free -m" (as root) and read "available" |
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mike155
Advocate
Joined: 17 Sep 2010
Posts: 4438
Location: Frankfurt, Germany
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| Posted: Sun Dec 19, 2021 2:26 am Post subject: |
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@megalodon: Linux uses RAM to cache files.
Let's take a look at the output of 'free' on my machine
| Code: | $ free
total used free shared buff/cache available
Mem: 65199976 1316476 63472672 82796 410828 63266908
Swap: 0 0 0
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There's a 'free' value and an 'available' value.
Let's read a large file to fill a part of the cache:
| Code: | $ dd if=~/large_file >/dev/null
$ free
total used free shared buff/cache available
Mem: 65199976 1286328 55110984 82552 8802664 63289256
Swap: 0 0 0
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The 'free' value goes down, but 'available' doesn't change.
Let's clear the caches:
| Code: | $ sync; echo 3 >/proc/sys/vm/drop_caches
$ free
total used free shared buff/cache available
Mem: 65199976 1301864 63488296 82764 409816 63281080
Swap: 0 0 0
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The 'free' value is back to it's original value.
If you want to compare memory consumption, use the 'available' values. Alternatively, you could clear caches and use the 'free' values. |
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