Re: [lc-devel] Swap lockup in 2.4.17pre7

[Rodrigo S. de C. <rc...@im...>]

On Fri, Jan 25, 2002 at 12:04:05AM +0800, David Chow wrote:
> After download the new pre7 patch for 2.4.17 . It seems I am having the
> same problem. The machine locks up when swap usage go to around 20MB .
> My machine is PIII having 512MB of swap space, runing 16384 pages of
> compressed cache with a total of 256MB of RAM . When under load with
> swap space usage around 10%, the machine will freeze, after freeze the
> harddisk will still scratch for a while and making noise.

David,

Could you please test with 0.21 final version I just released? I
noticed a stupid bug concerning vswap that can make things work over
there.

There is a variable to assure that vswap is conservative when
assigning new vswap address. The point is that we can't have many
vswap address that haven't been compressed, otherwise we may fill up
the compressed cache (since we can't predict how big the fragment will
be) and thus can't store this fragment. Well, this variable was
supposed to be signed, so we would have negative values e when its
value is below 0, we have to stop returning vswap address in some
scenarios. However I declared it as unsigned long (duh), so vswap
would return all available addresses if requested, what's totally
wrong. If many addresses are assigned, the likeliest is to panic (the
panic in mm/comp_cache/swap_out.c), locking up your machine. It's
fixed in 0.21.

I tested this patch for over 12 hours on a real machine and under UML,
swapping out over 90 MiB in the former and 32 MiB in the latter, and
it survived. :-)

Thanks,
-- 
Rodrigo S. de Castro <rc...@im...>