Re: filecache/swapcache questions

[Andrea Arcangeli <andrea@suse.de>]

On Mon, 21 Jun 1999, Kanoj Sarcar wrote:

>And continuing on with the problems with swapoff ...

I have not thought yet at the races you are talking about in the thread.

But I think I seen another potential problem related to swapoff in the
last days. Think if you run swapoff -a while there is a program that is
faulting in a swapin exception. The process is sleeping into
read_swap_cache_async() after having increased the swap-count (this is the
only problem). While the task is sleeping swapoff will swapin the page and
will map the swapped-in page in the pte of the process while the process
is sleeping. Then swapoff continue and see that the swap-count is still >
0 (1 in the example) even if the page is been swapped-in for all tasks in
the system. Swapoff get confused and set the swap count to 0 by hand (and
doing that it corrupts a bit the state of the VM). I think I reproduced
the above scenario stress testing 2.3.8 + my VM changes (finally "stable"
except the buffer beyond end of the device problem) but it the problem
I seen is real then it will apply to 2.2.x as well.

Andrea Arcangeli

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