Dec 26, 2020 3:47:44 PM Frantisek Rysanek <frantisek.rysa...@post.cz>:
> I've noticed that you want to have about 4 times the swap space > compared to physical RAM. This means to me that your historical > machine is starved of RAM, and you envisage enhancing the volume of > RAM by a quick swap space. Hmm. > The actual success of that idea will depend on how large your typical > "DRAM working set" actually is. Actually I anticipate swap usage at about double physical RAM (for a total memory usage of 3x physical RAM). I'm using Debian to administer the machine (with DOS/Win95 for actual retrocomputing), and empirically that runs well (shell only) with that amount of swap (at least with the swap partition on a magnetic disk). If I start XFCE, then it starts thrashing, but I don't really need a graphical environment there. > It gets worse. If your machine thrashes the swap space intensively, > generating lots of those tiny write transactions, a typical CF card > will quickly get its relatively tiny transaction buffer (and "SLC > zone", if used) full of pending writes and will slow down noticeably > at the outer ATA interface. Don't be surprised to see 25 IOps or even > less, pauses lasting a couple seconds etc. A pretty far cry from > those ~4k IOps that you might come to expect, based on random read > performance. 25 IOps doesn't sound good. How does that compare to a similar I/O pattern on a late 90s/early 2000s magnetic disk? > > Try comparing your CF-based swap-on-flash solution with an > alternative setup, using some SATA-based SSD/CFast/mSATA > and a SATA/IDE converter. How about converting this all the way to a > small Optane drive :-) Those have like 6k of permitted overwrites, if > memory serves - and have really short latencies. Except that ehh... > they seem to be NVMe = PCI-e based, rather than SATA. Ahh well. Well, the absolute ideal for swap, if I could find it, would be an IDE device that used a couple GiB of modern DRAM and initialized itself at boot from some partitioning plan (for instance "1 Linux swap partition", or "1 Linux swap partition, 1 empty FAT partition"), or an image on a read only flash device. There's no need for a swap device to actually be non-volatile (beyond keeping formatting information for the OS to recognize it as a swap device), and DRAM doesn't have write limits. > I can't seem to find any figure, how much RAM your machine actually > has, just that you want 4 times that much in swap. As above, I'm not going for quite 4x RAM for swap, but the exact numbers in the current magnetic disk configuration are 40 MiB RAM, 80 MiB swap, and I plan to overprovision swap significantly on CF to spread out write wear. Part of what I'm trying to figure out is what kind of overprovisioning I'll need to get a decent lifetime for the swap device. > I actually wanted to say this: if you > only have use for maybe 1 GB of swap, it's no problem that your > partition can only be 2 GB, Actually only 512 MiB for anything DOS will be touching (or when BIOS first sees the drive), but that won't be a problem for the Linux swap partition once I've done the whole "trick the BIOS" dance. _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
