On Mon, 2020-06-08 at 22:54 +0000, Konstantin Kharlamov wrote: > > On Sat, Jun 6, 2020 at 10:00 AM Richard W.M. Jones > > <rjones(a)redhat.com> wrote: > > > > (ZRAM) > > Compression is intrinsic to just the /dev/zram device. The swap > > code > > doesn't share pages between swap devices. The higher priority > > device > > is favored first until full. Once full, pages don't go through the > > zram module, thus are not compressed, on their way to the > > swap-on-disk. > > > > (ZSWAP) > > So yeah, the swap-on-disk scenario might be better suited to a > > generator that could use zswap instead, which uses an existing swap > > partition and adds a write back cache (zpool) rather than a > > separate > > device. I'm pretty sure (not 100%) that cached page are > > decompressed > > on their way to the swap device. Also, the zpool memory cache is > > preallocated, unlike zram devices. > > > > (I am not going to envy any who decide to implement zswap on a > > system > > with ZFS. Wait wait wait, which zpool are you talking about?!) > > So, I am testing ZRAM right now (as per your advice in another > thread). All well > so far, however reading this makes me think I gonna stumble upon a > point where > ZSRAM will be a better fit. > > You see, the idea of ZRAM and ZSWAP is improving low-memory > situation. This is > especially relevant for small amount of RAM, like your Raspberry > example. > > In such situation if you, for example, open a lot of tabs in a > browser, you may > easily get to a point where even ZRAM is exhausted. Now, had you > additionally a > SWAP device, it would be no problem, the data would simply spill over > to SWAP. > > Yes, SWAP is slow (well, it is on HDD at least). But consider this: > in this > workload , you most likely not gonna touch older of browser tabs for > quite some > time, so the slowness won't hurt you. > > My point is that we still need disk swap. And if we have disk swap, > we'd want to > move into SWAP the most unused memory pages. Which is how it works > with > ZSWAP. But not how it works with ZRAM (in which case, as you noted, > once it's > full, all new data would simply go past ZRAM into disk SWAP) > > --------- > > Now, I love the idea of using either ZRAM or ZSWAP. But to consider > which one of > them do we want, I think we would need to discuss first: do we really > want to get > rid of disk swap? Hibernation being discussed somewhere in this > thread is another > point. I personally don't like idea of removing disk swap. I should've added: browsing the Internet and watching video/reading social networks, and perhaps playing some browser games in their spare time, is a common activity for many people. I.e. the workload mentioned should be popular enough to take into consideration. _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
