Den 20-Mar-00 14:19:28 skrev James Sutherland fĝlgende om "Re: Overcommitable memory??":
> On 20 Mar 2000 1:8:46 +0100, you wrote:
>> Actually, just having overcommitment turned off will itself tend to keep
>>a little memory free for someone to log in and sort out the situation.
>>Let's say the system is down to 500 kB of free memory (RAM+swap) and a
>>program requests 600 kB. Now, without overcommitment of memory, the
^^^^^^^^^^^^^^^^^^^^^^^^
>>allocation will fail and the system will still have 500 kB of free memory
^^^^^^^^^^^^^^^^^^^^
>>left, all your daemons will still be running, etc.
> No; malloc() still fails, because the 600K allocation exceeds free VM.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Why do we suddenly agree about this part? A misunderstading?
[cut]
>>2) An application accesses a part of its allocated address space and the
>>kernel can't handle it because all RAM and swap has been used. This can
>>only happen when the kernel has overcommitted memory. Short of suspending
>>the currently running process until memory is freed, there isn't much the
>>kernel can do except to kill a process and free memory that way.
> Why had the process allocated unused memory anyway?
Like, because it never got a chance to use it after allocating it?
> In the normal case
> (allocate a buffer, then use it) overcommit never comes into play.
Race condition. Linux is a multitasking system. Think of two or more
processes.
> It
> is only if you malloc() a fairly large buffer (a few K or more) and
> then do not use it until much later that there is a potential problem.
Where "much later" can be anything from a timeslice and up. Even if you
memset() straight away, too bad Linux decided to give the CPU(s) to other
processes. Linux is a multitasking system.
(We've been through the rest a couple of times already.)
Regards,
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This archive was generated by hypermail 2b29 : Thu Mar 23 2000 - 21:00:34 EST