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SubjectRe: [2.4.17/18pre] VM and swap - it's really unusable
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2.4.17rc2aa2 seems to handle the grow/shrink of buffer_head,
dentry_cache, inode_cache slabs and page/buffer caches pretty
well.

Machine has 1GB RAM and CONFIG_NOHIGHMEM=y
1027 MB swap.

root# dmesg|grep Mem
Memory: 901804k/917504k available (1049k kernel code, 15312k reserved, 259k data, 236k init, 0k highmem)
root# uptime
2:47pm up 4 days, 17:04, 12 users, load average: 1.00, 1.00, 1.00

# Run updatedb to expand the size of dentry_cache.
root# updatedb

# At first, slabs are fairly large.
root# egrep 'inode_cache|dentry_cache|buffer_head' /proc/slabinfo
inode_cache 469072 469168 512 67024 67024 1
dentry_cache 539651 539670 128 17989 17989 1
buffer_head 119438 126330 128 4211 4211 1
Machine has been up for a while, compiling things, running tests, etc,
so page and buffer caches are large too. That's expected/desireable
as there is no memory shortage.

root# free -mt
total used free shared buffers cached
Mem: 880 868 11 0 152 316
-/+ buffers/cache: 400 480
Swap: 1027 0 1027
Total: 1908 868 1039

# count processes
root# ps axu|wc -l
64
# allocate and write to 99% of virtual memory
root# time ./mtest01 -p 99 -w
Filling up 99% of ram which is 1855075778d bytes
PASS ... 1855979520 bytes allocated.

real 0m39.006s
user 0m8.610s
sys 0m7.170s

# notice how much the slabs shrank compared to above.
root# egrep 'inode_cache|dentry_cache|buffer_head' /proc/slabinfo
inode_cache 254 658 512 94 94 1
dentry_cache 193 1140 128 38 38 1
buffer_head 8609 43650 128 1455 1455 1
# Memory allocated to buffers/cache has decreased considerably too.
root# free -mt
total used free shared buffers cached
Mem: 880 71 809 0 29 6
-/+ buffers/cache: 35 845
Swap: 1027 27 1000
Total: 1908 98 1810

# no processes killed by OOM
root# ps aux|wc -l
64
# Now force an OOM condition
root# time ./mtest01 -p 101 -w
Filling up 101% of ram which is 1916602941d bytes
Killed

real 0m40.083s
user 0m8.770s
sys 0m7.270s

Note the time to notice and kill mtest01 because of OOM is short.
39 seconds to allocate 1855979520 bytes of VM.
40 seconds to allocate 1916602941 bytes and kill with OOM handler.

# Only mtest01 killed by OOM
root# ps axu|wc -l
64
In the experiment above, it appears the rc2aa2 VM shinks slabs and
page/buffer caches in a reasonable way when a process needs a lot
of memory.

--
Randy Hron

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