[gentoo-amd64] Is swap need when there is 4g of ram?

[gentoo-amd64] Is swap need when there is 4g of ram?

[P.V.Anthony]

Hi,

Is swap really needed when there is a 4g of ram?

P.V.Anthony
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Hemmann, Volker Armin]

On Dienstag, 13. März 2007, P.V.Anthony wrote:
> Hi,
>
> Is swap really needed when there is a 4g of ram?

depends ;)

but you don't need a swap partition. A swapfile is good enough and more 
flexible.
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Joaquim Quinteiro Uchoa]

My 50 cents:

A swap partition is always faster than a swap file. Not so much, but is faster.
With 4GB of RAM is expected to find computers with lof of free space in hard
disk. So: creating a 4GB of swap in a partition will give us a extra
resource with
little cust.

Anthony is really right: it depends if you need swap. In a server with
30 users,
problably not, even in the case where the access is simultaneous (by experience
with servers with 2GB of RAM and 2GB of swap).

But, in a desktop, it depends of applications running at the same time. I have
4 GB  of RAM, and when emerging some large programs, I mount some part of
memory (3GB) in /var/tmp/portage (using tmpfs). This acelerates the emerging
process, and the only program I can't compile in this way is openoffice :(.

When I'm using memory as a space to compile programs, the swap is used
in some moments, if I'm using firefox (with 2 windows of 10 tabs each) and
openoffice.

So, in normal use, you probably don't need a swap. But, It will hurts in terms
of disk space to create it? Probably not, so create and be prepared to large
requests of memory :). This is my sugestion...


2007/3/13, Hemmann, Volker Armin <volker.armin.hemmann@tu-clausthal.de>:
> On Dienstag, 13. März 2007, P.V.Anthony wrote:
> > Hi,
> >
> > Is swap really needed when there is a 4g of ram?
>
> depends ;)
>
> but you don't need a swap partition. A swapfile is good enough and more
> flexible.
> --
> gentoo-amd64@gentoo.org mailing list
>
>


-- 
[]s
Joaquim
------------------------------------------
  (o_    Joaquim Quinteiro Uchoa
 //\        Consultor Linux e EaD
 U_/_    Linux User # 100534
------------------------------------------
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Hemmann, Volker Armin]

On Dienstag, 13. März 2007, Joaquim Quinteiro Uchoa wrote:
> My 50 cents:
>
> A swap partition is always faster than a swap file. Not so much, but is
> faster. 

nope. That was only true for 2.2 and 2.4 kernels. One of the features of 2.6 
is that swapfiles are not slower anymore.

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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[dustin]

On Tue, Mar 13, 2007 at 09:46:39AM -0300, Joaquim Quinteiro Uchoa wrote:
> Anthony is really right: it depends if you need swap. In a server with
> 30 users,
> problably not, even in the case where the access is simultaneous (by experience
> with servers with 2GB of RAM and 2GB of swap).

One of the benefits of swap is that unused application text, data, etc.
can be paged out in a fairly permanent fashion.  Without swap, that
stuff has to sit in RAM, even if it's not touched for hours or days.

I'm not sure if your load is such that the savings will be a significant
portion of 4G.

Dustin
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Joaquim Quinteiro Uchoa]

Ok, new swapfiles are acessed as block, bypassing the filesystem:

http://lkml.org/lkml/2005/7/7/326

In this way, with physical access, really doesn't matter if is a
partition or a swapfile...

In this situation, a swap partition is only more easy to manage (You
don't need to
create the file after the instalation proccess) and can be shared by
several SOs in a
same computer. But swapfiles can be more flexible (you can expand and move more
easily).

I think I will prefer swapfiles in future instalations :)


2007/3/13, Hemmann, Volker Armin <volker.armin.hemmann@tu-clausthal.de>:
> On Dienstag, 13. März 2007, Joaquim Quinteiro Uchoa wrote:
> > My 50 cents:
> >
> > A swap partition is always faster than a swap file. Not so much, but is
> > faster.
>
> nope. That was only true for 2.2 and 2.4 kernels. One of the features of 2.6
> is that swapfiles are not slower anymore.
>
> --
> gentoo-amd64@gentoo.org mailing list
>
>


-- 
[]s
Joaquim
------------------------------------------
  (o_    Joaquim Quinteiro Uchoa
 //\        Consultor Linux e EaD
 U_/_    Linux User # 100534
------------------------------------------
--
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[gentoo-amd64] Re: Is swap need when there is 4g of ram?

[Duncan]

"P.V.Anthony" <pvantony@singnet.com.sg> posted
45F66A32.1050004@singnet.com.sg, excerpted below, on  Tue, 13 Mar 2007
17:09:06 +0800:

> Is swap really needed when there is a 4g of ram?

As VAH says, depends.

I ran without swap with a gig of RAM for some time.  That was generally 
enough for me.  Only one time did I actually run out of memory, when I 
tried to scan a larger than really necessary image at too high a 
resolution and color depth.  However...

There are several reasons to run swap.  It's likely that at least one of 
the following will apply.

Less so with current kernels, but it wasn't that long ago (certainly well 
into the 2.6 series, maybe 2.6.12-ish?) that the kernel had no direct way 
to switch memory between different "memory zones".  There could be plenty 
of memory, but memory of a specific type, say in the PCI 32-bit direct 
DMA zone (up to 4 gig, but note that due to the memory hole for it at 
just below 4 gig, 4 gigs of actual memory will map a quarter to a half a 
gig above the 4 gig memory barrier) could be tight, with no way to 
rearrange things that could otherwise be moved elsewhere into other 
memory zones, without using the "backing store" of swap.  Put simply, 
swap gave the kernel more flexibility in how it managed memory, a 
flexibility that could be useful at times. 

Eventually, the kernel hackers implemented a way to transfer memory 
between zones without resorting to backing store (aka swap), so this no 
longer applies to modern kernels per se, but the general idea of 
flexibility continues to.  Disabling swap entirely kills the kernel's 
ability to memory-map a file on disk without reading it into physical 
memory.  This actually doesn't use the swap space, just maps the file 
where it is into memory without actually reading it into memory.  There 
are times when this is more efficient than actually reading the whole 
thing into memory, and disabling swap (as in turning off the virtual 
memory option before compiling the kernel, I believe it can still do it 
if the option is on but no swap space is actually allocated, tho I'm not 
positive on that) kills this flexibility.

OK, so those don't apply to a modern kernel in many operational 
circumstances.  It's nice to have the flexibility, but...  Still, there 
are other reasons to keep swap around.

There's a balance between cache and swap.  With swap turned off, data and 
memory for all running apps, including those that don't actually run very 
much (say print services on a system where something's actually printed 
perhaps once or twice a week on average), /must/ be maintained in real 
memory.  What's used for such applications cannot be used for caching 
files so they don't actually have to be read off disk once they are read 
the first time.  If you generally never top off memory and cache to the 
point where the system is throwing away cache to keep memory, and with 4 
gig, you may not, unless you use some of the tricks below, it doesn't 
matter so much, but the minute you start throwing away cache to keep 
stuff like a seldom used CUPS print system in memory, because you have 
swap disabled, you begin to slow down your next read of the cached data 
you just threw away.

BTW, with swap enabled, there is a knob you can tweak that sets the 
kernel's balance between keeping apps vs. keeping cache in memory, when 
one or the other needs dumped in ordered to make room for something just 
coming in.  /proc/sys/vm/swappiness defaults to a generally reasonable 
60, IIRC, but can be set to anything between 0 and 100.  Here, I'm 
running a reasonably fast RAID system with 4-way striped swap, and a 4-
spindle RAID-6, effectively making it two-way striped.  Since swap is 
four-way striped while my main system is only two-way striped, swap 
should be faster than reading stuff back in from the RAID-6, so as part 
of my boot sequence I "echo 100 > /proc/sys/vm/swappiness".  That means 
the kernel will /always/ prefer keeping cache, dumping the least used 
applications to swap where necessary.  Conversely, people who run a 
single hard drive with both swap and most of their filesystem on it, who 
run an slocate updatedb cron job over night and come back to a really 
sluggish system the next morning because the kernel has swapped all their 
still loaded firefox tabs and the like out in favor of caching what 
amounts to the single-shot updatedb data, may wish to set swappiness 
lower than the default 60, say 20, or even 0, at which point the system 
would always favor the apps and always dump cache, when it came to that 
point.

However, the BIG payoff of lots of memory (4 gig or so being a sweet spot 
for this), particularly for Gentoo systems or anyone else doing a lot of 
"temp" work, compiling or the like, is to setup a large (several gig) 
tmpfs and do all your compiling and stuff there, only copying the 
completed files over to the main non-volatile filesystem.  On Gentoo, 
it's particularly easy to use a tmpfs for compiling and the like, by 
simply setting the appropriate PORTAGE_TMPDIR and similar variables in 
make.conf.  With "only" four gig of memory, however, and with certain 
packages requiring sizable work areas (OOo is said to require on the 
order of 4-5 gigs!), trying this without swap risks severe memory 
shortage situations.  I have a full 8 gig memory and a 5 gig tmpfs /tmp 
(with portage pointed to it) here, and even with 8 gigs memory, if I try 
emerging several things in parallel, it's not unusual to see active swap 
as a result.  On a four gig system, I'd DEFINITELY want swap backup if I 
had PORTAGE_TMPDIR and friends pointed at tmpfs (which I might then try 
at 3 GB max size, tho obviously that wouldn't work if I tried to compile 
OOo or something nearly as big).

It's worth repeating.  A tmpfs based PORTAGE_TMPDIR is probably the 
single best use for 4 gig of memory on a normal Gentoo system, but it's 
not something I'd recommend anyone try without swap.  Therefore, I'd 
recommend a tmpfs be setup for portage to use, and that swap remain 
enabled for the system to use in the event it needs it when portage is 
compiling something big.  To try to setup that tmpfs for portage to use 
/without/ swap enabled... might be OK on an 8 gig system tho I'm not 
going to try it myself, but is certainly risking trouble and instability 
on a 4 gig system.

Finally, note that the in-kernel hibernate (aka suspend to disk) 
functionality requires a dedicated swap partition of sufficient size.  
Suspend to disk is /finally/ working here, and it's a nice feature to 
have.  However, it /does/ require swap space to suspend into.  (Note that 
the swap partition doesn't have to be the full size of RAM.  Each of my 
swap stripes is only 4 gig, making 16 gig of swap available, but suspend 
will only use one stripe, so 4 gig.  I have 8 gig memory but only a 4 gig 
swap stripe partition to suspend to, but it works fine.)  If you are 
using a non-vanilla kernel with the Suspend2 patch, or something similar, 
this may or may not apply, as I think it's possible for it to use a non-
swap suspend file.  However, with the mainline in-kernel suspend, at 
least last I read, it requires swap.  That's actually why I re-enabled 
swap here, tho it was quite some time before I could actually get suspend 
to disk to actually work as advertised.  I kept swap enabled and would 
try it every few kernel versions, and it finally started working!

So in summary, four reasons to keep swap enabled:

1) Old kernels needed it for memory zone management.  (N/A for a decently 
modern kernel, say 2.6.16 or newer.)

2) Memory mapped file flexibility.

3) tmpfs based PORTAGE_TMPDIR and friends is generally a MUCH more 
efficient use of several gigs of memory than turning off swap, but until 
you have I'd say 6 gigs memory minimum, you'll want to keep swap enabled 
if you do it.

4) Suspend to disk, aka hibernate, uses swap.

#3 and possibly #4 are the important ones.

OTOH, disabling swap entirely, by turning off that config option in 
kernel setup before compiling it, DOES significantly simplify kernel code 
and memory management.  This was in fact the reason I had it off back 
when I had only a gig of memory.  I had system stability issues due to 
unstable memory hardware (cheap memory) at the time, and I figured the 
less complicated kernel memory management was, the more stable the system 
was likely to be.  I don't know if it made much of a difference, but it 
definitely wasn't LESS stable.  (The memory zone issues did apply back 
then, but my hardware simply wasn't stable enough for that to be much of 
an issue.)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Hemmann, Volker Armin]

On Dienstag, 13. März 2007, dustin@v.igoro.us wrote:
> On Tue, Mar 13, 2007 at 09:46:39AM -0300, Joaquim Quinteiro Uchoa wrote:
> > Anthony is really right: it depends if you need swap. In a server with
> > 30 users,
> > problably not, even in the case where the access is simultaneous (by
> > experience with servers with 2GB of RAM and 2GB of swap).
>
> One of the benefits of swap is that unused application text, data, etc.
> can be paged out in a fairly permanent fashion.  Without swap, that
> stuff has to sit in RAM, even if it's not touched for hours or days.
>

no it has not to stay in ram. Unused stuff that is not 'dirty' IE identical to 
the stuff on harddisk, can be kicked out of ram, when the space is needed.

And for some funny reason, loading something out of swap is much slower than 
loading it from the fs....

50mb in swap - and everything is slow. So slow as if every bit is fetched by a 
mule caravan. And it does not matter if it is a swap partition or a swap 
file. It is slow. 

But there is an easy way to get the box back to normal speed: swapoff -a && 
swapon -a ...
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Hemmann, Volker Armin]

On Dienstag, 13. März 2007, Joaquim Quinteiro Uchoa wrote:
> Ok, new swapfiles are acessed as block, bypassing the filesystem:
>
> http://lkml.org/lkml/2005/7/7/326
>
> In this way, with physical access, really doesn't matter if is a
> partition or a swapfile...
>
> In this situation, a swap partition is only more easy to manage (You
> don't need to
> create the file after the instalation proccess) and can be shared by
> several SOs in a
> same computer. But swapfiles can be more flexible (you can expand and move
> more easily).
>
> I think I will prefer swapfiles in future instalations :)
>

I have a (small) swap partition, and a big 'emergeny' swapfile - that is 
hardly ever used.
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Peter Humphrey]

On Tuesday 13 March 2007 09:09:06 P.V.Anthony wrote:
>
> Is swap really needed when there is a 4g of ram?

Yes.

That assumes that you will be compiling lots of large programs such as 
mozilla-firefox and Open Office. Let me tell you about my case:

I have 4 GB RAM and 2 x Opteron 246 CPUs, and I have three 2GB swap 
parttions: one each on 2 x IDE and 1 x SATA disks. I've told portage to use 
the /tmp directory for its work, and /tmp is mounted on tmpfs with a size 
of 6.5 GB. If /tmp occupancy outgrows the physical RAM, the kernel swaps 
part of it out to disk and carries on. Magic!

I run top in an X terminal when I want to monitor swap use. It shows me that 
the only time the swap gets used is when I'm compiling one of those large 
packages. Open Office, in particular, uses up to 5.7 GB of temporary space 
on my box, which is why I've set the /tmp limit to 6.5 GB. It may actually 
use more, but that's the most I've observed.

This box also spends nearly all its cycles on BOINC projects 
(http://boinc.berkeley.edu/), which not only ramps up the temp and noise, 
but of course uses a fair amount of space. All the same, I still don't see 
any use of swap except on those prodigious compiling jobs.

So, if you don't intend to compile large packages, you probably don't need 
swap; if you do, you do.

HTH.

-- 
Rgds
Peter Humphrey
Linux Counter 5290, Aug 93
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Richard Freeman]

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Hemmann, Volker Armin wrote:
> And for some funny reason, loading something out of swap is much slower than 
> loading it from the fs....

That seems odd.  if you're talking about executables and other MMAP'ed
objects the filesystem IS the swap (when apache needs to be swapped out
the kernel just deletes it from memory and reloads from disk - unless
the executable pages were modified - not sure how dynamic linking is
handled in linux, and if that needs to modify code pages).

Unless of course your swap is encrypted or something it should be faster
than the FS...

> 
> 50mb in swap - and everything is slow. So slow as if every bit is fetched by a 
> mule caravan. And it does not matter if it is a swap partition or a swap 
> file. It is slow. 
> 

I haven't seen this behavior - I routinely have maybe 500MB swapped out.
 The difference is that most of this is probably tmpfs data that isn't
touched until tmpreaper comes around and deletes it.

The critical factor is probably RSS - if you have a zombie process that
uses 1GB of RAM and which sleeps for 3 days at a time (with NO activity)
then if you swap it out there is probably no impact.  On the other hand,
if you have 50 processes all running with 2%CPU each and they each have
a 100MB RSS and you have 1GB of RAM your system will come to a complete
halt.  Even if all combined they only need 1.1GB of RAM you'll probably
still come to a halt since they'll be constantly churning that 100MB of
swap.  If 100MB worth  of processes sleep suddenly the whole system will
wake up.

Basically, there is no fix for lots of RUNNING processes other than more
RAM (or not running everything at once).  But lots of idle processes do
just fine with swap.

And not having a swap partition doesn't stop swapping.  Any time you
mmap a file you have virtual memory - no getting around it.  And that
data will get swapped in and out as needed.  And even if none of your
software uses mmap the kernel does every time it loads an image.  It
greatly improves performance (unused code never gets loaded).

If I'm wrong on any of this kindly point it out, but this is my
understanding of how linux swapping works.
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Jack Lloyd]

On Tue, Mar 13, 2007 at 03:32:45PM +0100, Hemmann, Volker Armin wrote:

> 50mb in swap - and everything is slow. So slow as if every bit is fetched by a 
> mule caravan. And it does not matter if it is a swap partition or a swap 
> file. It is slow. 
> 
> But there is an easy way to get the box back to normal speed: swapoff -a && 
> swapon -a ...

Perhaps better to tweak the VM so it is not as swap-happy using
/proc/sys/vm/swappiness. See http://kerneltrap.org/node/1044
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Hemmann, Volker Armin]

On Mittwoch, 14. März 2007, Jack Lloyd wrote:
> On Tue, Mar 13, 2007 at 03:32:45PM +0100, Hemmann, Volker Armin wrote:
> > 50mb in swap - and everything is slow. So slow as if every bit is fetched
> > by a mule caravan. And it does not matter if it is a swap partition or a
> > swap file. It is slow.
> >
> > But there is an easy way to get the box back to normal speed: swapoff -a
> > && swapon -a ...
>
> Perhaps better to tweak the VM so it is not as swap-happy using
> /proc/sys/vm/swappiness. See http://kerneltrap.org/node/1044

swappiness does not help, if swap is really needed (like when compiling 
kdepim). The 'stupid' thing is, as soon as swap is used, it stays that way, 
no matter how many hundred mb of ram are free.
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Bernhard Auzinger]

> swappiness does not help, if swap is really needed (like when compiling
> kdepim).

I did not reconize yet that kdepim is that hungry at compile time :).

> The 'stupid' thing is, as soon as swap is used, it stays that way, 
> no matter how many hundred mb of ram are free.

The reason for that behaviour is, that in my opinion it would be nonsense to 
delete things from the swap when there is enough swap space free. But I think 
you can be sure that if there is enough ram free that the things will also be 
in the ram again. Things are kept (duplicated) in the swap space if there is 
enough swap because it's faster when it's necessary to swap out the same 
things again, I think.

That's just a theory. I don't know for sure if I'm right.

rgds
Bernhar
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Hemmann, Volker Armin]

On Mittwoch, 14. März 2007, Bernhard Auzinger wrote:
> > swappiness does not help, if swap is really needed (like when compiling
> > kdepim).
>
> I did not reconize yet that kdepim is that hungry at compile time :).
>
j2 for MAKEOPTS and +kdeenablefinal and after some time each one of the 
makejobs want 900mb ram. There are two libs where that happens, makes kdepim 
the slowest-to-compile packet for me. Wesnoth is also an offender. Some 
versions want 500mb+ at some point when compiling.
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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Bernhard Auzinger]

> j2 for MAKEOPTS and +kdeenablefinal and after some time each one of the
> makejobs want 900mb ram. There are two libs where that happens, makes
> kdepim the slowest-to-compile packet for me. Wesnoth is also an offender.
> Some versions want 500mb+ at some point when compiling.

That's pretty much. About 3 years ago I watched a similar behaviour on PyQt. 
At that time I had just 512MB of ram (and a 1.2GHz pentium3) and that tiny 
package drove me crazy because the memory requested by gcc when compiling 
PyQt was more than 512MB and the compile process did not only happen on data 
stored in the ram but also on data stored in the swap space. It was awful. My 
system was not usable for more than an hour. It was so busy swapping as I 
never saw a system swapping before. I remember that after a upgrade to 1G ram 
the PyQt package took less than five minutes. I decided to trace the memory 
usage when compiling PyQt and I recognized that it was less than a minute 
requesting so much memory. That was the first time I was convinced that 
swapping can end very very bad.

rgds
Bernhard

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Re: [gentoo-amd64] Is swap need when there is 4g of ram?

[Paul de Vrieze]

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On Tuesday 13 March 2007, Joaquim Quinteiro Uchoa wrote:
> Ok, new swapfiles are acessed as block, bypassing the filesystem:
>
> http://lkml.org/lkml/2005/7/7/326
>
> In this way, with physical access, really doesn't matter if is a
> partition or a swapfile...

Except that for a swap partition all parts of it are certainly contiguous. 
Something that does not generally hold for swap files. Being contiguous could 
help the speed a bit.

Paul

-- 
Paul de Vrieze
Gentoo Developer
Mail: pauldv@gentoo.org
Homepage: http://www.devrieze.net

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[gentoo-amd64] Re: Is swap need when there is 4g of ram?

[Duncan]

"Hemmann, Volker Armin" <volker.armin.hemmann@tu-clausthal.de> posted
200703142003.11766.volker.armin.hemmann@tu-clausthal.de, excerpted below,
on  Wed, 14 Mar 2007 20:03:11 +0100:

> j2 for MAKEOPTS and +kdeenablefinal and after some time each one of the
> makejobs want 900mb ram. There are two libs where that happens, makes
> kdepim the slowest-to-compile packet for me. Wesnoth is also an
> offender. Some versions want 500mb+ at some point when compiling.

In general c++/g++ is FAR more memory and CPU intensive than gcc 
compiling C.  I look at it this way (non-technical explanation), the OOP 
functionality of C++ is a great productivity enhancement for programmers, 
making them more effective.  However, the tradeoff is that it makes the 
compiler work harder doing all the stuff automatically that the 
programmer didn't do manually.

For those of us using split KDE packages rather than the monolithic 
versions, kmail is the particular part of kdepim that requires the huge 
resources.  With USE=kdeenablefinal (which is designed for file 
distribution level compilation, and turns on a bunch of compile resource 
expensive optimizations to make run-time performance as good as 
possible), on AMD64 at least, one specific compile job in that package 
requires over a gig of memory at one particular point.  Anybody who has 
only a gig of memory WILL be in swap at that point, there's no way around 
it except to USE=-kdeenablefinal for that package, setting it in 
package.use or whatever.

It'd be interesting to be enough of a programmer to figure out exactly 
what's requiring all that memory, but it's beyond my rather limited 
capacities in that area, so...

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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Re: [gentoo-amd64] Re: Is swap need when there is 4g of ram?

[P.V.Anthony]

On this day, 13-March-2007 10:30 PM,  Duncan wrote:
> So in summary, four reasons to keep swap enabled:
> 
> 1) Old kernels needed it for memory zone management.  (N/A for a decently 
> modern kernel, say 2.6.16 or newer.)
> 
> 2) Memory mapped file flexibility.
> 
> 3) tmpfs based PORTAGE_TMPDIR and friends is generally a MUCH more 
> efficient use of several gigs of memory than turning off swap, but until 
> you have I'd say 6 gigs memory minimum, you'll want to keep swap enabled 
> if you do it.
> 
> 4) Suspend to disk, aka hibernate, uses swap.
> 
> #3 and possibly #4 are the important ones.
> 
> OTOH, disabling swap entirely, by turning off that config option in 
> kernel setup before compiling it, DOES significantly simplify kernel code 
> and memory management.  This was in fact the reason I had it off back 
> when I had only a gig of memory.  I had system stability issues due to 
> unstable memory hardware (cheap memory) at the time, and I figured the 
> less complicated kernel memory management was, the more stable the system 
> was likely to be.  I don't know if it made much of a difference, but it 
> definitely wasn't LESS stable.  (The memory zone issues did apply back 
> then, but my hardware simply wasn't stable enough for that to be much of 
> an issue.)

Thank you to all for advising on the swap issue. The information is very 
useful and has helped me to make a decision. I am happy.

For the record, I am going with swap file of 4g.

Once again thank you all for the advice.

P.V.Anthony

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