After a “find” operation spanning the entire disk, I suddenly had System Monitor (2.28.0 of Fedora 12) telling me that 11.5 GB out of the existing 16 GB were used up, and the applet said 75% was “in use by programs”. Really. Virtually nothing was running on the system.
Just to be sure, I tried out
$ ps aux --sort -rss | less
(list processes sorted by resident memory) and as expected, no memory hog to be seen.
So what does the kernel (a home cooked 2.6.35.4) say for itself?
$ cat /proc/meminfo MemTotal: 16463436 kB MemFree: 130568 kB Buffers: 2818532 kB Cached: 1387344 kB SwapCached: 0 kB Active: 3368176 kB Inactive: 2246912 kB Active(anon): 1407872 kB Inactive(anon): 339276 kB Active(file): 1960304 kB Inactive(file): 1907636 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 368 kB Writeback: 0 kB AnonPages: 1409264 kB Mapped: 174032 kB Shmem: 337932 kB Slab: 10246976 kB SReclaimable: 9526744 kB SUnreclaim: 720232 kB KernelStack: 5112 kB PageTables: 47880 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 8231716 kB Committed_AS: 4241756 kB VmallocTotal: 34359738367 kB VmallocUsed: 122564 kB VmallocChunk: 34359572612 kB HardwareCorrupted: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 350080 kB DirectMap2M: 16422912 kB
Hmmm… That’s the kernel eating up ~10 GB, most of which is reclaimable. This page seems to explain the issue: As the disk was scanned, directory and inode metadata was probably cached. So what if that takes nearly 10 GB?
The thing is that it gives a somewhat misleading picture of the computer’s state.
So let’s just tell the kernel to drop all those caches, as suggested in that page:
As root, just go
# echo 3 > /proc/sys/vm/drop_caches
and watch how the memory meter drops. This problem is supposed to be solved in kernel not as ancient as mine.