Large memory support

[Jason Titus]

Actually, this was on RedHat Enterprise Linux 64 on a dual Opteron =
system.  No matter what I entered as a memory size, it listed 2GB as =
maxbytes in STATS.  When I added more records after it reached 1.9GB it =
would start tossing things.

When I replaced the unsigned ints with unsigned long longs, it would =
grow past 2GB.

Seems like switching to size_t would be the best path.  What do you =
think?

Jason

p.s. - Our goal is to have a ~5GB cache with an entire database.  We =
want to disable expiration (i.e. nothing getting removed out of the =
cache) and have the cache be the definitive read only source.  It would =
have a syncing process to keep it up to date with any changes.

-----Original Message-----
From: Brad Fitzpatrick [mailto:brad@danga.com]
Sent: Wed 2/18/2004 9:37 PM
To: Jason Titus
Cc: memcached@lists.danga.com
Subject: Re: Large memory support
=20
Jason,

I've built and run memcached on 64-bit machines.

On a 32-bit machine you won't be able to store more memory than your
operating system is giving you address space for.  (Not sure if
your OS is giving you a 2G/2G, 3G/1G, or 3.5G/0.5G split)

I assume you're on 32-bit?  Otherwise, isn't an "unsigned long" just a
uint64 on 64-bi machines?  Or should we be using void* somewhere we're
using unsigned int?

Let me know your OS, arch, and the contents of "stats maps" (if on =
Linux):

$ telnet localhost 11211
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
stats maps
08048000-08050000 r-xp 00000000 03:03 2167117    =
/usr/local/bin/memcached-1.1.10pre2
08050000-08051000 rw-p 00008000 03:03 2167117    =
/usr/local/bin/memcached-1.1.10pre2
08051000-09c02000 rwxp 00000000 00:00 0
40000000-40011000 r-xp 00000000 03:03 165006     /lib/ld-2.3.1.so
40011000-40012000 rw-p 00011000 03:03 165006     /lib/ld-2.3.1.so
40017000-4011f000 r-xp 00000000 03:03 165009     /lib/libc-2.3.1.so
4011f000-40125000 rw-p 00107000 03:03 165009     /lib/libc-2.3.1.so
40125000-40128000 rw-p 00000000 00:00 0
40128000-40131000 r-xp 00000000 03:03 165014     =
/lib/libnss_compat-2.3.1.so
40131000-40132000 rw-p 00009000 03:03 165014     =
/lib/libnss_compat-2.3.1.so
40132000-40142000 r-xp 00000000 03:03 165013     /lib/libnsl-2.3.1.so
40142000-40143000 rw-p 00010000 03:03 165013     /lib/libnsl-2.3.1.so
40143000-80946000 rw-p 00000000 00:00 0
bfffc000-c0000000 rwxp ffffd000 00:00 0
END


- Brad


On Wed, 18 Feb 2004, Jason Titus wrote:

> Looks like we just stumbled onto some 32 bit limits in memcached.  =
Just
> wondering how you guys want to deal with supporting >2GB per cache.  =
We
> have experimented with switching some of the unsigned ints into =
unsigned
> long longs and it seemed to work (>4GB seemed ok.  No thorough testing
> yet though).  A cleaner solution might be adjusting the memory related
> variables to size_t or some such so that they work well on 32 and 64 =
bit
> systems.
>
> What makes the most sense to you folks?
>
> Jason
>
>