Re: some memory/swap thoughts
Jan Gyselinck (JAN.GYSELINCK@student.kuleuven.ac.be)
Wed, 18 Mar 1998 17:00:46 +0100 (W. Europe Standard Time)
On Wed, 18 Mar 1998, Andreas Kostyrka wrote:
> On Wed, 18 Mar 1998, Jan Gyselinck wrote:
> > Now, 5 meg as a cache, isn't that too much?? Some people think this is
> Nope, I routinly run with 80MB swap (here and at home.) And it's a
> difficult question, because there are tradeoffs: Either you want one bzip
> to run fast, or you want a dozen bzip par. run with high troughput.
I can't run a dozen bzip's with high troughput if I only have 16 meg RAM
> (That's nicely demonstrated by EIDE/SCSI on a multiuser server: Replacing
> a 5 yrs old SCSI disc with a new EIDE that was in benchmarks 3-4 times
> faster resulted in grinding teh server to a halt. I had to replace EIDE
> disc with a new SCSI disc, which again in benchmarks is about 50-60% of
> the speed of the EIDE disc, but I can do background kernel recompiles
> without anyone even noticing :) ).
Yes, and my HD is slow, I know.
> > needed, well I can tell you, it isn't. A year ago, I did some testing on
> > a 486DX33 with 8 meg, running DOS/winslows 3.11. I tried different
> > cache-sizes (with pc-cache) and measured the speedup while starting up
> Comparing the Linux cache subsystem to SMARTDRV is like doing performance
> testing on LADA and then applying the findings to BMW/Cadillac/... They
> may hald true, but they may hold also not true!
It wasn't smartdrive, it was pc-cache, that's somewhat better :p
> > MS-Word. Maybe you think that's not the way to test this, but why not?
> > You test the speed-up in real-life applications, because that's what you
> > do all day. So, speedup from 0 to 64 kB cache, 20 seconds, from 64 to 128
> > kB cache, 14 seconds, from 128 to 256 kB, 6 seconds, from 256 to 512 kB, 3
> > seconds, and from 512 to 1024 kB, 1 second. Now why in gods name would
> Again, on a Single-User box a different memory management may seem better.
> (But what happens if the single-user becomes a power user and begins to
> ``multitask'' heavily?)
Maybe that's true. I only know that things were different (and maybe you
can't notice that on that speed-monster of yours)
> > one want 5 meg of cache? It will increase the speed of disk-activity with
> > maybe 1 second of a 2,5 meg cache. My oppinion is that for 16 meg of
> > memory, the minimum-limit for a disk-cache should be 256kB, not 5 meg!!
> Nope, that sucks. I know how NeXT with 800kb-2MB cache runs on the same
> hardware as Linux. Limiting the cache is not a very clever thing.
I was talking about the minimum cache size, not the maximum. At the
moment, on my machine, minimum cache size is 5 meg, and that's toooo much
> > Okay, you say, but what about all those idling programs that are stuck in
> > memory, and just take up memory from the cache. I know, I know, there are
> > cases where it's needed to run such programs, but not always. People are
> > running to many idle programs these days! Why do you think there is a
> Nope. By definitation a process that does a sleep(3600); should not be a
> hurden on the system. -> That's usual POSIX coding understanding.
> And not all can be handled by inetd, and not all should be handled.
> > inet-daemon? So that there don't need to be a dozen idle processes who
> > are checking if there isn't something knocking on there port. Running 6
> They are not checking. They are blocked. And that means they are eligible
> for swapping.
> > or more agetty's? There exists something like a console spawn daemon, you
> Nice. And what if each of the ``getty's'' does a different thing? (One
> menu for system halt/restart/etc., one menu to restart gpm [Did you notice
It was an example, every case and environment is different.
> it's quite impossible to find GOOD 3 button trackballs today, especially
> if you don't want to pay MEGABUCKs? I've got one here, that seems to
> ``powerdown'' and needs to be restarted with button pressed, ...]
I got one too, and it functions without problems.
> > If I run a bash on a console, and I do something on another console for a
> > while, and I return to the first one, I want the bash-process to respond
> > immediatly to my key-strokes. I don't like to wait for it until it's
> > loaded from swap. My opinion is this: if I run something, it is because
> > it needs to run, and it must be able to respond immediatly. If this is
> But Linux is Unix and by definition is a server OS. If you want a buggy
> scheduler implementation, than go buy OS/2 or NT *g*. (I've seen a nice
> SQL server for OS/2, but the scheduler was quite broken: It automatically
> decreased the priority of the server if you minimized it. So the Server
> had to run in foreground all the time, ...)
So you actually _like_ having a slow OS?? I began with 1.2.13 on my
portable, and that was _fast_. Previous linux kernels didn't do such
aggressive memory-freeing.
> > not so, I wont run it. I don't have memory to throw around, I need every
> > bit. (And no, memory for a portable is not that cheap)
> Than you want to use it more cleverly than to have say 900kb wasted on
> bash blocked on read(0,..,..);
900kB? It's shared, maybe 500 kB is not shared. I want my system to swap
if it's needed, not to have some more cache. Disks are quite fast now,
and they cache a bit too.
> > So think about this, when you people change something in the
> >memory-management of linux, because it'll run on low-budget and
> > high-budget systems...
> The point is, that Linux is as a server OS more optimized for the
> multitasking/multiuser troughput. And that's the complicated one: If you
> want to run one thing a time, than DOS quite cut it :)
??
My point is: don't swap if it is not needed. Like I said, I do
multi-task!
>
> > Jan Gyselink
> > for the moment a swapping linux-user
> Nothing bad about swapping. (And running bzip on a underpowered machine
> was always painful. If it wouldn't be so painful, than bzip would have
> long replaced gzip, right?)
No? My machine doesn't respond when it swaps! And that's bad.
I got not that much diskspace either, and bzip used to run fine.
> > PS: i hope .90 is better, 'll try it tonight, but after I rebooted,
> > because my console is messed up by Xwindows, who didn't restore the state
> > after it finished (maybe caused by to much swapping?????)
> Why should swapping influence this? *wonder*
Euh, maybe because things got stalled???
> Andreas
Jan Gyselinck
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