Re: running Linux with no swap space (but lots of RAM)

phil-news-nospam@xxxxxxxx writes:

[...]

| e> In that situation it is quite likely that you don't have "some
| e> other device" to swap to. That's probably why you are booting
| e> from flash in the first place.
|
| The problem in your new hypothetical is then that you have no device
| capable of tolerating paging I/O, not that the system is paging to
| disc.

Please explain what you mean by "tolerating paging I/O".

In plain words, this means 'only devices whose actual behaviour and
limitations the OP understands even less well than he believes to
understand disks'.

[...]

A frequent scenario I see happens when my need for memory by user space
programs is below the capacity is available, and would not have even begun
to swap anything. A program is run that will be doing a large amount of
I/O output, such as copying 100+ GB of files between filesystems. The I/O
buffering goes beyond just the pages that are free. The buffering logic
tries to buffer far more of those 100+ GB than needed to keep the writing
drive continuously busy or even to minimize head seeks.

The purpose of the page cache is neither 'to keep the drive
continously busy' nor 'to minimze head seeks'. Both would be tasks the
elevator (or I/O-scheduler) is supposed to accomplish.

The end result is that other programs that were not immediately in
use (for example Firefox, Thunderbird, and even Xorg itself), get
substantially swapped out.

'programs' (ie text pages corresponding to running processes) are
never 'swapped out', because the corresponding memory pages are
usually clean, so their contents can be discarded and later re-read
from disk.

Just for an informal test, I have just created an archive of all of my
filesystem to /dev/null (~16G). The amount of memory allocated to
'buffers' and 'cached' (vmstat) peaked well below 95000K and 45000K,
respectively. No paging activities occured during creation of the
archive.

BTW, the by-and-far easiest path to personal happiness for you in this
respect is to just misconfigure your system to your hearts content
(its yours, after all) instead of talking about hypothesises you have
about situations which - for some strange reason - are not that
generally reproducible than the generality of your inferences would
require.

It would still be more sensible to add RAM until you don't experience
regular paging activities occuring for some unknown reason on your
system and leave the virtual memory configuration as-is to deal with
non-regular situations. Or consider reducing your working set.
.

Relevant Pages

  • Re: MALLOC
    ... Paging isn' treally a good model, for the reason you point out. ... I/O would suffice (we use multimedia I/O calls, which work on structured files, and can ... >exceptions on access to uncommitted memory. ... >be to allocate pagefile space in 64 KB chunks, ...
    (microsoft.public.vc.mfc)
  • Perofmance / Paging Question
    ... be a large number of page faults: ... I/O Reads: 11K ... So, why all the paging? ... to tune the system to allow this application to take more memory? ...
    (microsoft.public.win2000.general)
  • Re: Apps swapped out without swap or what?
    ... and I HAVE NO SWAP PARTITION in this computer! ... minute of inactivity or so, the shell had problems responding, I had to ... load pages or otherwise allocate memory. ... might be suffering from conflicting I/O, ...
    (alt.os.linux)
  • Re: Do I need a Page File?
    ... paging out physical memory or not. ... Can I do that or does Windows XP really need the ... > require the paging file, ... > unlimited amounts of RAM, we wouldn't even NEED a paging file. ...
    (microsoft.public.windowsxp.general)
  • Re: MAssive Performance hit after AIX 4.3 -> 5.2 upgrade!!
    ... i think AIX has a sort of pre-emptive paging system that makes it ... > start to page in/out unless it is running low on memory. ... > You can post 'svmon' output here because it is short. ...
    (comp.unix.aix)