Quoting Daniel de Kok <danieldk@xxxxxxxxx>:
On Wed, 2006-08-16 at 16:08 -0500, Aleksandar Milivojevic wrote:
Hmmm... Any downside to setting it to 0?
Yeah. It disables the OOM killer, possibly leading to the situation
where no one can allocate memory. Having it enabled (and set to one
process) will try to pick a process according to the least surprise
principle.
So, does "no one can allocate memory" means:
a) things will be put on hold until kswapd frees enough pages (if
possible, than apps will start dying), or
b) the machine will freeze
The (a) is what usually happens on other operating system (Tru64
and/or Solaris). And it is acceptable. If backing store is
overallocated, and free swap falls to zero, kernel kills userland
process that it can't handle anymore. However, as I said many times
in this thread, this is not what happened in my case. I had more than
enough free space on swap to accomodate offending application.
Node 0 Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB
0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
Node 0 HighMem: empty
Seems like a very bad OOM situation. Remember that the swapper is not
just an extension of physical memory, since kswapd has to take care of
paging out memory pages. If you are allocating huge chunks of memory in
a short time, you may want to crank up the vm.min_free_kbytes tunable.
This variable sets the low watermark of free memory, and setting it
higher gives the kernel more room for emergency allocations (e.g.
letting kswapd do its work). Setting it to 4096KB should help a lot,
though I have seen people setting it much higher on servers.
In my case, min_free_kbytes was set to 1015 (default, I guess). I'll
try crancking it up. Machine has 1 gig of memory, so there's plenty
of space to play with that parameter before performance will suffer
noticably. Anyhow, I'd expect that min_free_kbytes would be
performance tunable. Not something I'd need to touch to make machine
more stable.
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