2.0.34pre8-testing

Roman Drahtmueller (draht2@rzlin1.ruf.uni-freiburg.de)
Fri, 17 Apr 1998 01:05:29 +0200 (MEST)

When it comes to virtual memory, the Sun people tend to make no
difference between physical memory and swap. VM is VM, which makes my
X-server on Solaris vanish into dark swap swamp while the box is
seeking for buffer/cache space for disk i/o. Such behaviour might be
advantageous in some way (Sun ppl didn't tell anything convincing).
But I was not aware of the fact that linux behaves similarly, if not
intentionally, then accidentially (one or the other? Shouln't
buffering be the luxury of RAM?). With 2.0.29, buffers and cache usage
dropped down to almost zero if you did `dd if=/dev/zero of=/dev/null
bs=many_megs count=1'. After all buffers were gone, the box started
swapping. Doing so with 2.0.33+, there always remains some buffered
stuff in RAM, several megs, apparently pushing the rest ahead of it.
Does it allocate buffers instead of freeing them to give way?

Did anybody experience conditions that don't refer easily to
filesystem/block device activity among which mem gets lost at
increasing speed? I'm not sure if it's my personal uptime today if I
can't get those numbers together. Anyway, I thought it's worth
mentioning: According to the manpage, `free' gets its information from
/proc/meminfo. I find the outputs that I have attached at the end
somewhat strange. There might be just a different understanding about
what is "buffer". But still there is little in common.

Btw, I never got 2.0.33 to crash. Only swapping to death made it die
predictably. It only got slow due to mem leak(s). Ah, where is this
memleak-deluxe stuff hidden on the net?

Here are the contradictory outputs. Enlighten me about dumbness if I
missed the point or see if you can verify this behaviour.
45908 kB in -/+ buffers/cache: this number barely decreases. Usually
it just eats up until its number is near to the physical mem
installed. Also interesting: A summary over all resident mem sizes may
very well give more than twice the amount of memory installed.

# free # box has 80 MB RAM installed.
total used free shared buffers cached
Mem: 78636 76552 2084 25388 7864 22780
-/+ buffers/cache: 45908 32728
Swap: 175000 47920 127080

# cat /proc/meminfo
total: used: free: shared: buffers: cached:
Mem: 80523264 78401536 2121728 25972736 8052736 23330816
Swap: 179200000 49070080 130129920
MemTotal: 78636 kB
MemFree: 2072 kB
MemShared: 25364 kB
Buffers: 7864 kB
Cached: 22784 kB
SwapTotal: 175000 kB
SwapFree: 127080 kB

Another box, 128 MB mem installed, almost no swap activity, serves
mail and http, up 70 days. The box' RSS fields sum'd up gives a total
of 217 MB (!).

# free
total used free shared buffers cached
Mem: 127776 125164 2612 191860 35280 48700
-/+ buffers: 41184 86592
Swap: 232868 376 232492
# cat /proc/meminfo
total: used: free: shared: buffers: cached:
Mem: 130842624 128172032 2670592 196435968 36126720 49868800
Swap: 238456832 385024 238071808
MemTotal: 127776 kB
MemFree: 2608 kB
MemShared: 191832 kB
Buffers: 35280 kB
Cached: 48700 kB
SwapTotal: 232868 kB
SwapFree: 232492 kB

Roman
Drahtmüller.

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