Re: VM balancing problems under 2.4.2-ac1

[Mike Galbraith]

On Sun, 4 Mar 2001, Ingo Oeser wrote:

> On Sat, Mar 03, 2001 at 01:03:26AM +0100, Adrian Bunk wrote:
> > > If anybody as a good idea to make this code auto-balancing,
> > > please let me know.
> >
> > I have no idea for auto-balancing but another idea: It's one possibility
> > to let the user choose when doing "make *config" what he wants:
> >
> > - A VM optimized for servers that swaps out applications in favor of
> >   caching.
> > or
> > - A VM optimized for workstations that won't swap out applications in
> >   favor of caching.
>
> I thought about the same thing sometimes (but for other troughput
> vs. latency decisions, too).
>
> But I realized, that my very own workstation is also a server,
> since it runs an httpd, mysqld, smbd, ftpd etc.
>
> And somtimes the servers become very busy in our LAN[1].
>
> IF we want that tuning, we should have it as a sysctl. Most of it
> is already possible with /proc/sys/vm/*, but balancing decisions
> are still missing.

I think sysctls for balancing knobs is a great idea.  The VM has no
clue concerning the cost of rebuilding cache eg but a human may.

Automatic tuning would be wonderful, but it requires information
which the VM flat doesn't have.. so it should ask the boss for help.

Three handy knobs I can think of off the top of my head are swap_size,
flush_size [for page_launder().. bdflush has that] and cache_stickiness.

-Mike

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Re: VM balancing problems under 2.4.2-ac1

[Ingo Oeser]

On Sat, Mar 03, 2001 at 01:03:26AM +0100, Adrian Bunk wrote:
> > If anybody as a good idea to make this code auto-balancing,
> > please let me know.
> 
> I have no idea for auto-balancing but another idea: It's one possibility
> to let the user choose when doing "make *config" what he wants:
> 
> - A VM optimized for servers that swaps out applications in favor of
>   caching.
> or
> - A VM optimized for workstations that won't swap out applications in
>   favor of caching.

I thought about the same thing sometimes (but for other troughput
vs. latency decisions, too).

But I realized, that my very own workstation is also a server,
since it runs an httpd, mysqld, smbd, ftpd etc.

And somtimes the servers become very busy in our LAN[1].

IF we want that tuning, we should have it as a sysctl. Most of it
is already possible with /proc/sys/vm/*, but balancing decisions
are still missing.

And even for servers we need to reduce caching sometimes. Think
of an httpd serving _very_ dynamic content. Or any other
application (e.g. DMBS), that doesn't rely on file system
caching.

A anonymous/file-backed[2] ratio would be VERY handy ;-)

But maybe this will be implemented one day along the lines of QoS
in the VM...

Regards

Ingo Oeser

[1] >1500 possible clients for these servers.
[2] Not counting swaps as file backed. We have a special inode
   for the swapper anyway, right?
-- 
10.+11.03.2001 - 3. Chemnitzer LinuxTag 
    come and join the fun   
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Re: VM balancing problems under 2.4.2-ac1

[Ingo Oeser]

On Sat, Mar 03, 2001 at 01:03:26AM +0100, Adrian Bunk wrote:
  If anybody as a good idea to make this code auto-balancing,
  please let me know.
 
 I have no idea for auto-balancing but another idea: It's one possibility
 to let the user choose when doing "make *config" what he wants:
 
 - A VM optimized for servers that swaps out applications in favor of
   caching.
 or
 - A VM optimized for workstations that won't swap out applications in
   favor of caching.

I thought about the same thing sometimes (but for other troughput
vs. latency decisions, too).

But I realized, that my very own workstation is also a server,
since it runs an httpd, mysqld, smbd, ftpd etc.

And somtimes the servers become very busy in our LAN[1].

IF we want that tuning, we should have it as a sysctl. Most of it
is already possible with /proc/sys/vm/*, but balancing decisions
are still missing.

And even for servers we need to reduce caching sometimes. Think
of an httpd serving _very_ dynamic content. Or any other
application (e.g. DMBS), that doesn't rely on file system
caching.

A anonymous/file-backed[2] ratio would be VERY handy ;-)

But maybe this will be implemented one day along the lines of QoS
in the VM...

Regards

Ingo Oeser

[1] 1500 possible clients for these servers.
[2] Not counting swaps as file backed. We have a special inode
   for the swapper anyway, right?
-- 
10.+11.03.2001 - 3. Chemnitzer LinuxTag http://www.tu-chemnitz.de/linux/tag
come and join the fun   
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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Re: VM balancing problems under 2.4.2-ac1

[Mike Galbraith]

On Sun, 4 Mar 2001, Ingo Oeser wrote:

 On Sat, Mar 03, 2001 at 01:03:26AM +0100, Adrian Bunk wrote:
   If anybody as a good idea to make this code auto-balancing,
   please let me know.
 
  I have no idea for auto-balancing but another idea: It's one possibility
  to let the user choose when doing "make *config" what he wants:
 
  - A VM optimized for servers that swaps out applications in favor of
caching.
  or
  - A VM optimized for workstations that won't swap out applications in
favor of caching.

 I thought about the same thing sometimes (but for other troughput
 vs. latency decisions, too).

 But I realized, that my very own workstation is also a server,
 since it runs an httpd, mysqld, smbd, ftpd etc.

 And somtimes the servers become very busy in our LAN[1].

 IF we want that tuning, we should have it as a sysctl. Most of it
 is already possible with /proc/sys/vm/*, but balancing decisions
 are still missing.

I think sysctls for balancing knobs is a great idea.  The VM has no
clue concerning the cost of rebuilding cache eg but a human may.

Automatic tuning would be wonderful, but it requires information
which the VM flat doesn't have.. so it should ask the boss for help.

Three handy knobs I can think of off the top of my head are swap_size,
flush_size [for page_launder().. bdflush has that] and cache_stickiness.

-Mike

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Re: VM balancing problems under 2.4.2-ac1

[Adrian Bunk]

On Fri, 23 Feb 2001, Rik van Riel wrote:

> On 23 Feb 2001, Adam Sampson wrote:
>
> > The VM balancing updates in the recent ac kernels seem to have caused
> > some interesting performance problems on my desktop machine. I've got
> > 160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
> > amounts of it for buffers and cache while pushing stuff out to
> > swap. This means that Mozilla, for instance, runs significantly worse
> > than under 2.4.0, since bits of it are being swapped in and out.
>
> This is a known problem which I'll fix as soon as I have a
> solution.
>
> The problem is that we still have no good way to balance
> how much memory we take from the cache and how much memory
> we take from processes.

I have the same problem Adam has: I'm running 3-5 applications on my
computer. I have 64 MB of RAM and I use usually less than 50 MB. I have
swap for the rare cases where I need more RAM than I have. But with
2.4.x-acyz kernels I do often have to wait several seconds after I
switched to another running application before it's swapped in again
because it seems this application was swapped out to cache some MP3 I
surely won't listen to before the next reboot...

> This means that for some workloads we'll be evicting too
> much cache while for other workloads we'll be evicting too
> much process pages...
>
> If anybody as a good idea to make this code auto-balancing,
> please let me know.

I have no idea for auto-balancing but another idea: It's one possibility
to let the user choose when doing "make *config" what he wants:

- A VM optimized for servers that swaps out applications in favor of
  caching.
or
- A VM optimized for workstations that won't swap out applications in
  favor of caching.


I know that's not a perfect solution but it would make the situation much
better.


> regards,
>
> Rik

cu
Adrian

-- 

Nicht weil die Dinge schwierig sind wagen wir sie nicht,
sondern weil wir sie nicht wagen sind sie schwierig.

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Re: VM balancing problems under 2.4.2-ac1

[Adrian Bunk]

On Fri, 23 Feb 2001, Rik van Riel wrote:

 On 23 Feb 2001, Adam Sampson wrote:

  The VM balancing updates in the recent ac kernels seem to have caused
  some interesting performance problems on my desktop machine. I've got
  160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
  amounts of it for buffers and cache while pushing stuff out to
  swap. This means that Mozilla, for instance, runs significantly worse
  than under 2.4.0, since bits of it are being swapped in and out.

 This is a known problem which I'll fix as soon as I have a
 solution.

 The problem is that we still have no good way to balance
 how much memory we take from the cache and how much memory
 we take from processes.

I have the same problem Adam has: I'm running 3-5 applications on my
computer. I have 64 MB of RAM and I use usually less than 50 MB. I have
swap for the rare cases where I need more RAM than I have. But with
2.4.x-acyz kernels I do often have to wait several seconds after I
switched to another running application before it's swapped in again
because it seems this application was swapped out to cache some MP3 I
surely won't listen to before the next reboot...

 This means that for some workloads we'll be evicting too
 much cache while for other workloads we'll be evicting too
 much process pages...

 If anybody as a good idea to make this code auto-balancing,
 please let me know.

I have no idea for auto-balancing but another idea: It's one possibility
to let the user choose when doing "make *config" what he wants:

- A VM optimized for servers that swaps out applications in favor of
  caching.
or
- A VM optimized for workstations that won't swap out applications in
  favor of caching.


I know that's not a perfect solution but it would make the situation much
better.


 regards,

 Rik

cu
Adrian

-- 

Nicht weil die Dinge schwierig sind wagen wir sie nicht,
sondern weil wir sie nicht wagen sind sie schwierig.

-
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Re: VM balancing problems under 2.4.2-ac1

[Mike Galbraith]

On Fri, 23 Feb 2001, Rik van Riel wrote:

> If anybody as a good idea to make this code auto-balancing,
> please let me know.

(I haven't seen even one suggestion posted.. must be a real bugger)

I haven't found any silver bullets ;) but the one line bend-adjust
below does help the cache problem a little on my wimpy 128mb box.

Worth trying out on other boxen with other loads?  It doesn't get
swap in/out to a 1:1 ratio, but does improve it considerably by
scanning a larger portion of active pages prior to swapout.

(the other two lines are there only because it seemed reasonable;)

-Mike

against 2.4.2-ac4

--- mm/vmscan.c.org Mon Feb 26 09:31:46 2001
+++ mm/vmscan.c Mon Feb 26 16:32:46 2001
@@ -278,6 +278,8 @@
/* Always start by trying to penalize the process that is allocating memory */
if (mm)
retval = swap_out_mm(mm, swap_amount(mm));
+   if (retval)
+   return retval;

/* Then, look at the other mm's */
counter = (mmlist_nr << SWAP_SHIFT) >> priority;
@@ -846,7 +848,7 @@
  * continue with its real work sooner. It also helps balancing when we
  * have multiple processes in try_to_free_pages simultaneously.
  */
-#define DEF_PRIORITY (6)
+#define DEF_PRIORITY (2)
 static int refill_inactive(unsigned int gfp_mask, int user)
 {
int count, start_count, maxtry;

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Re: VM balancing problems under 2.4.2-ac1

[Mike Galbraith]

On Fri, 23 Feb 2001, Rik van Riel wrote:

 If anybody as a good idea to make this code auto-balancing,
 please let me know.

(I haven't seen even one suggestion posted.. must be a real bugger)

I haven't found any silver bullets ;) but the one line bend-adjust
below does help the cache problem a little on my wimpy 128mb box.

Worth trying out on other boxen with other loads?  It doesn't get
swap in/out to a 1:1 ratio, but does improve it considerably by
scanning a larger portion of active pages prior to swapout.

(the other two lines are there only because it seemed reasonable;)

-Mike

against 2.4.2-ac4

--- mm/vmscan.c.org Mon Feb 26 09:31:46 2001
+++ mm/vmscan.c Mon Feb 26 16:32:46 2001
@@ -278,6 +278,8 @@
/* Always start by trying to penalize the process that is allocating memory */
if (mm)
retval = swap_out_mm(mm, swap_amount(mm));
+   if (retval)
+   return retval;

/* Then, look at the other mm's */
counter = (mmlist_nr  SWAP_SHIFT)  priority;
@@ -846,7 +848,7 @@
  * continue with its real work sooner. It also helps balancing when we
  * have multiple processes in try_to_free_pages simultaneously.
  */
-#define DEF_PRIORITY (6)
+#define DEF_PRIORITY (2)
 static int refill_inactive(unsigned int gfp_mask, int user)
 {
int count, start_count, maxtry;

-
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Re: VM balancing problems under 2.4.2-ac1

[Rik van Riel]

On Sat, 24 Feb 2001, Joseph Bueno wrote:
> Rik van Riel a écrit :
> > On 23 Feb 2001, Adam Sampson wrote:
> >
> > > The VM balancing updates in the recent ac kernels seem to have caused
> > > some interesting performance problems on my desktop machine. I've got
> > > 160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
> > > amounts of it for buffers and cache while pushing stuff out to
> > > swap. This means that Mozilla, for instance, runs significantly worse
> > > than under 2.4.0, since bits of it are being swapped in and out.
> >
> > This is a known problem which I'll fix as soon as I have a
> > solution.
> >
> > The problem is that we still have no good way to balance
> > how much memory we take from the cache and how much memory
> > we take from processes.

> I understand that auto-balancing code that deals with all
> situations is very hard to design; so let me share my experience
> on other Unix systems (from a user/administrator point of view):
>
> I have used Unix systems (mainly HPUX) for several years as personal
> workstations or servers and buffer cache usage were very differents:
>
> On workstations, you are mainly looking for fast interactive response
> time and  you want to dedicate as much memory as possible to running
> processes so limiting buffer cache to 10% of physical memory (these
> workstations had typically 32 - 64 Mb of RAM) was good.

"Unfortunately" the cache also contains _process memory_ in
Linux. Limiting the cache to 10% also means limiting the
code size of all your processes to something smaller than
that.

Also, read-in swap pages are in the so-called swap cache,
which is also part of the page cache.

This means that simple limits on cache size probably won't do
much good on Linux.

regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

http://www.surriel.com/
http://www.conectiva.com/   http://distro.conectiva.com.br/

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Re: VM balancing problems under 2.4.2-ac1

[Joseph Bueno]

Rik van Riel a écrit :
> 
> On 23 Feb 2001, Adam Sampson wrote:
> 
> > The VM balancing updates in the recent ac kernels seem to have caused
> > some interesting performance problems on my desktop machine. I've got
> > 160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
> > amounts of it for buffers and cache while pushing stuff out to
> > swap. This means that Mozilla, for instance, runs significantly worse
> > than under 2.4.0, since bits of it are being swapped in and out.
> 
> This is a known problem which I'll fix as soon as I have a
> solution.
> 
> The problem is that we still have no good way to balance
> how much memory we take from the cache and how much memory
> we take from processes.
> 
> This means that for some workloads we'll be evicting too
> much cache while for other workloads we'll be evicting too
> much process pages...
> 
> If anybody as a good idea to make this code auto-balancing,
> please let me know.
> 
> regards,
> 
> Rik
> --
> Virtual memory is like a game you can't win;
> However, without VM there's truly nothing to lose...
> 
> http://www.surriel.com/
> http://www.conectiva.com/   http://distro.conectiva.com.br/
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to [EMAIL PROTECTED]
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Hi Rik,

I understand that auto-balancing code that deals with all
situations is very hard to design; so let me share my experience
on other Unix systems (from a user/administrator point of view):

I have used Unix systems (mainly HPUX) for several years as personal
workstations or servers and buffer cache usage were very differents:

On workstations, you are mainly looking for fast interactive response
time and  you want to dedicate as much memory as possible to running
processes so limiting buffer cache to 10% of physical memory (these
workstations had typically 32 - 64 Mb of RAM) was good.

On file servers, interactive response time is much less important than
file/network througput. In this case, having 80% of RAM used for buffer
cache is good and you may even want to not let it go below 50% even if
it slows down some batch processes.

Both cases were easily handled by 2 HPUX kernel tunable parameters that
defined minimum and maximum number of pages that could be used by the
buffer cache.
This could be implemented on Linux via /proc. I know it is already done
for minimum limit (in 2.2, I have no experience with 2.4 yet).
I have found some situations where not being able to force a maximum
limit was a problem.

You could argue that with a good load balancing algorithm user
defined limits are useless. Believe me, my experience on HPUX
workstations showed that lowering its max. limit from 50% (default
value) to 10% turned some sluggish machines into speed daemons !

Just my 0.02$
Hope this helps
--
Joseph Bueno
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Re: VM balancing problems under 2.4.2-ac1

[Joseph Bueno]

Rik van Riel a crit :
 
 On 23 Feb 2001, Adam Sampson wrote:
 
  The VM balancing updates in the recent ac kernels seem to have caused
  some interesting performance problems on my desktop machine. I've got
  160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
  amounts of it for buffers and cache while pushing stuff out to
  swap. This means that Mozilla, for instance, runs significantly worse
  than under 2.4.0, since bits of it are being swapped in and out.
 
 This is a known problem which I'll fix as soon as I have a
 solution.
 
 The problem is that we still have no good way to balance
 how much memory we take from the cache and how much memory
 we take from processes.
 
 This means that for some workloads we'll be evicting too
 much cache while for other workloads we'll be evicting too
 much process pages...
 
 If anybody as a good idea to make this code auto-balancing,
 please let me know.
 
 regards,
 
 Rik
 --
 Virtual memory is like a game you can't win;
 However, without VM there's truly nothing to lose...
 
 http://www.surriel.com/
 http://www.conectiva.com/   http://distro.conectiva.com.br/
 
 -
 To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
 the body of a message to [EMAIL PROTECTED]
 More majordomo info at  http://vger.kernel.org/majordomo-info.html
 Please read the FAQ at  http://www.tux.org/lkml/

Hi Rik,

I understand that auto-balancing code that deals with all
situations is very hard to design; so let me share my experience
on other Unix systems (from a user/administrator point of view):

I have used Unix systems (mainly HPUX) for several years as personal
workstations or servers and buffer cache usage were very differents:

On workstations, you are mainly looking for fast interactive response
time and  you want to dedicate as much memory as possible to running
processes so limiting buffer cache to 10% of physical memory (these
workstations had typically 32 - 64 Mb of RAM) was good.

On file servers, interactive response time is much less important than
file/network througput. In this case, having 80% of RAM used for buffer
cache is good and you may even want to not let it go below 50% even if
it slows down some batch processes.

Both cases were easily handled by 2 HPUX kernel tunable parameters that
defined minimum and maximum number of pages that could be used by the
buffer cache.
This could be implemented on Linux via /proc. I know it is already done
for minimum limit (in 2.2, I have no experience with 2.4 yet).
I have found some situations where not being able to force a maximum
limit was a problem.

You could argue that with a good load balancing algorithm user
defined limits are useless. Believe me, my experience on HPUX
workstations showed that lowering its max. limit from 50% (default
value) to 10% turned some sluggish machines into speed daemons !

Just my 0.02$
Hope this helps
--
Joseph Bueno
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
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Re: VM balancing problems under 2.4.2-ac1

[Rik van Riel]

On Sat, 24 Feb 2001, Joseph Bueno wrote:
 Rik van Riel a crit :
  On 23 Feb 2001, Adam Sampson wrote:
 
   The VM balancing updates in the recent ac kernels seem to have caused
   some interesting performance problems on my desktop machine. I've got
   160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
   amounts of it for buffers and cache while pushing stuff out to
   swap. This means that Mozilla, for instance, runs significantly worse
   than under 2.4.0, since bits of it are being swapped in and out.
 
  This is a known problem which I'll fix as soon as I have a
  solution.
 
  The problem is that we still have no good way to balance
  how much memory we take from the cache and how much memory
  we take from processes.

 I understand that auto-balancing code that deals with all
 situations is very hard to design; so let me share my experience
 on other Unix systems (from a user/administrator point of view):

 I have used Unix systems (mainly HPUX) for several years as personal
 workstations or servers and buffer cache usage were very differents:

 On workstations, you are mainly looking for fast interactive response
 time and  you want to dedicate as much memory as possible to running
 processes so limiting buffer cache to 10% of physical memory (these
 workstations had typically 32 - 64 Mb of RAM) was good.

"Unfortunately" the cache also contains _process memory_ in
Linux. Limiting the cache to 10% also means limiting the
code size of all your processes to something smaller than
that.

Also, read-in swap pages are in the so-called swap cache,
which is also part of the page cache.

This means that simple limits on cache size probably won't do
much good on Linux.

regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

http://www.surriel.com/
http://www.conectiva.com/   http://distro.conectiva.com.br/

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Re: VM balancing problems under 2.4.2-ac1

[Rik van Riel]

On 23 Feb 2001, Adam Sampson wrote:

> The VM balancing updates in the recent ac kernels seem to have caused
> some interesting performance problems on my desktop machine. I've got
> 160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
> amounts of it for buffers and cache while pushing stuff out to
> swap. This means that Mozilla, for instance, runs significantly worse
> than under 2.4.0, since bits of it are being swapped in and out.

This is a known problem which I'll fix as soon as I have a
solution.

The problem is that we still have no good way to balance
how much memory we take from the cache and how much memory
we take from processes.

This means that for some workloads we'll be evicting too
much cache while for other workloads we'll be evicting too
much process pages...

If anybody as a good idea to make this code auto-balancing,
please let me know.

regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

http://www.surriel.com/
http://www.conectiva.com/   http://distro.conectiva.com.br/

-
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Re: VM balancing problems under 2.4.2-ac1

[Rik van Riel]

On 23 Feb 2001, Adam Sampson wrote:

 The VM balancing updates in the recent ac kernels seem to have caused
 some interesting performance problems on my desktop machine. I've got
 160Mb of RAM, and 2.4.2-ac1 appears to be using excessively large
 amounts of it for buffers and cache while pushing stuff out to
 swap. This means that Mozilla, for instance, runs significantly worse
 than under 2.4.0, since bits of it are being swapped in and out.

This is a known problem which I'll fix as soon as I have a
solution.

The problem is that we still have no good way to balance
how much memory we take from the cache and how much memory
we take from processes.

This means that for some workloads we'll be evicting too
much cache while for other workloads we'll be evicting too
much process pages...

If anybody as a good idea to make this code auto-balancing,
please let me know.

regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

http://www.surriel.com/
http://www.conectiva.com/   http://distro.conectiva.com.br/

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