Re: Hibernation takes too long
What is the proportional size between RAM and swap?
On Sun, 2019-07-21 at 10:19 -0400, Stefan Monnier wrote:
> > Afaik it's advised to copy files to SSDs and not copy blockwise
> > (dd) because
> > layouts can differ very much and performance would suffer.
>
> As long as the filesystem is properly aligned on a 4KB boundary, I
> don't
> think there'll be any noticeable difference. I highly doubt this
> explains the 2 minutes needed to hibernate.
>
> > > At idle, only 1.2 Gb of RAM is occupied, so not all the 12GB
> > > should be
> > > moved to SSD.
> >
> > The 6 GB of RAM will be moved to the swap partition.
>
> No, only the occupied part of the RAM, and not even all of it (the
> parts that correspond to memory-mapped files (e.g. libraries and
> executables)) won't, for example. So we're likely taking about less
> than 1GB in this 1.2GB case.
>
> > That's why swap needs to be >= RAM for hibernating.
>
> Actually, this is neither necessary nor sufficient:
> - the RAM can't be saved into the part of the swap already used, so
> the
> rule should be "the unused part of the swap >= RAM" in order for
> the
> rule to be sufficient.
> - as mentioned about, not all the RAM needs to be saved to swap, and
> furthermore, hibernation usually compresses the data before saving
> it
> into the swap space, so it typically needs significantly less than
> the
> RAM (I'd expect a compression in the order of 3x).
>
> > The X61 will throttle SSD throughput as it has less bandwidth than
> > modern
> > SATA adapters. So, transferring those 6 GB
> > will take time...
>
> 1GB/3 is about 300MB, which shouldn't take more than 10s to save.
>
>
> Stefan
>
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