Re: Swap

[Michael <codejodler@gmx.ch>]

Hello, i'm interested in this topic too although i can't tell anything exciting new. But here's my opinion.

As for SSD specifics pls read https://wiki.archlinux.org/index.php/SSD it's a nice overview. As you can see, for SSD, any disk operation is 'bad' so you would try to put as much I/O as possible into RAM, for example avoid swapping and following Matus' aboce suggestions.

('bad' meaning that once all SSD cells are filled, the drive will become much slower. You may have noted the same effect with USB pen drives / memory sticks or SD cards.)

Between swap file or partition shouldn't be any notable performance difference. I want to make clear that swapping should not be required at all in the first place, on a decent system - if it really 'needs' swap then you either should upgrade your RAM memory, or if it's already pretty much, perhaps just don't worry: The kernel knows how to handle things. A massive amount of used up RAM includes, for example, applications that are already 'closed' but the data is simply kept because it's unnecessary additional work to remove. It's flagged as buffered (IIRR) and being available, that's all. You may have noted that a second launch of closed applications is faster, it does not include the same disk activity.

I went with laptops w/o any swap, before, and did not experience any immediate problems. Filling up 8G RAM with active process data, on a desktop system, is not that easy and probably happens  only if you never reboot and never close anything. (Which some poeple do.)

Hibernation. Like Stefan Monnier already pointed out, a compressed file of the active parts of RAM are stored, only (pls re-read his posting). It's quite impossible to have a hibernation file the same size as RAM, *if* your system didn't swap. In old days, with low RAM and regular swapping, on many systems, there could possibly have been swap data be included in the hibernation image, leading to bigger image size. I don't know and it's still hard to imagine.

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I'm especially interested in the question if and how swapfile works on SSD. I set up such a swapfile and had to give the exact blcok numbers in the kernel image option line. But someone on some mailing list suggested that on SSD these numbers can be shifted, and thus, hibernating could overwrite my presious user data. I lack the knowledge about filesystems on SSD.Does anyone know how that works out ?