Out of swap - NOT

[Mark Millard]

On 2017-Feb-13, at 7:20 PM, Konstantin Belousov <kostikbel at gmail.com> wrote:

> On Mon, Feb 13, 2017 at 04:46:04PM -0500, Brett Wynkoop wrote:
>> On Mon, 13 Feb 2017 15:55:11 -0500
>> Joe Nosay <superbisquit at gmail.com> wrote:
>> 
>>> Is it possible to place the swap on a separate disk such as a usb?
>> 
>> Yes, but I am not sure what difference that will make.  I would think a
>> swapfile is a swapfile.  Yes I am swapping on a file because the image
>> autogrew the filesystem on first boot, so no chance to set up a
>> partition.
> swapfile write requires the write request to come through the filesystem
> write path, which might require the filesystem to allocate more memory
> and read some data. E.g. it is known that any ZFS write request
> allocates memory, and that write request on large UFS file might require
> allocating and reading an indirect block buffer to find the block number
> of the written block, if the indirect block was not yet read.
> 
> As result, swapfile swapping is more prone to the trivial and unavoidable
> deadlocks where the pagedaemon thread, which produces free memory, needs
> more free memory to make a progress.  Swap write on the raw partition over
> simple partitioning scheme directly over HBA are usually safe, while e.g.
> zfs over geli over umass is the worst construction.

Thanks for the explanation of bugzilla 206038:

11.0-CURRENT -r293227 (and others) arm (rpi2/BeagleBone Black)
amd64 etc: swapfile usage hangs; swap partition works


I'll copy your text into the comments for that submittal.

===
Mark Millard
markmi at dsl-only.net