64bit 2.6.15.3 kernel not reporting free memory correctly?

From: Richard Wohlstadter
Date: Mon Mar 27 2006 - 11:20:27 EST

Hi,

I have some servers running 64-bit kernels with 8g of memory and from what I understand of linux kernel memory management, it does not look like free memory is being reported correctly after some large jobs have run over time. For instance, here is what one my servers are reporting right now:

$ free

total used free shared buffers cached
Mem: 8181360 5049828 3131532 0 243612 18256
-/+ buffers/cache: 4787960 3393400
Swap: 2048248 2496 2045752

$ cat /proc/meminfo

MemTotal: 8181360 kB
MemFree: 3131672 kB
Buffers: 243628 kB
Cached: 18308 kB
SwapCached: 0 kB
Active: 1126408 kB
Inactive: 3740400 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 8181360 kB
LowFree: 3131672 kB
SwapTotal: 2048248 kB
SwapFree: 2045752 kB
Dirty: 12 kB
Writeback: 0 kB
Mapped: 19764 kB
Slab: 164564 kB
CommitLimit: 6138928 kB
Committed_AS: 44092 kB
PageTables: 1064 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 263376 kB
VmallocChunk: 34359474699 kB

There are not many processes running right now, so I added all processes VmSize values which totals to: 332 meg

So the question is, if buffer/cache used totals 260meg and all processes running vmsize total 332 meg, then why is meminfo only reporting 3gig free. It seems that the kernel is keeping inactive pages from processes that have run in the past that are no longer running. I never see this type of issue on 32bit kernels so it seems this is 64-bit only(I've tried 2.6.14.3 and 2.6.15.3 kernels). Thanks to anyone who has any insight on this issue.

Rich Wohlstadter
Washington University of St. Louis
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/