Re: Very bad behavior of kswapd

[Rik van Riel]

On Wed, 18 Apr 2001, Laurent Chavet wrote:

> Try this (my example I've 2GB of ram)
>
> turn all your swap off
>
> dd about 15% of the size of your RAM:
> dd if=/dev/zero of=/local/test count=300 bs=1000000
>
> Run this program with SIZE about 95% of your RAM:
>
> #include <stdlib.h>
> #include <unistd.h>
> #include <assert.h>
>
> #define SIZE (1900 * 1024 * 1024)
> int main()
> {
>   int i;
>   char *p = malloc(SIZE);
>   assert (p != NULL);
>   for (i = 0; i < SIZE; i++)
>  p[i] = 1;
>   printf ("done %p\n", p);
>
>   while (1)
>   {
>  sleep (60);
>   }
>   return 0;
> }
>
>
> Watch top: when this program needs the memory that kswapd keep
> in cache they go both at 100% cpu (on SMP) but still the size of
> the program only grows at about 100KB/s, why is kswapd releasing
> it so slowly and taking so much CPU ?

Because kswapd still has to scan all the (unfreeable) memory
of the big process to determine it isn't freeable.

At the moment kswapd is really stupid about these corner-case
situations, please bear with us while we fix it ...

... and don't forget to fill in a bugzilla item on the
Linux-MM bugzilla ;)

regards,

Rik
--
Linux MM bugzilla: http://linux-mm.org/bugzilla.shtml

Virtual memory is like a game you can't win;
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