Andrew Morton wrote:

Nick Piggin [off-list ref] wrote:

quoted

 	background = (background_ratio * total_pages) / 100;
 	dirty = (dirty_ratio * total_pages) / 100;

Look, these are sysadmin-settable sysctls.  The admin can set them to
whatever wild and whacky values he wants - it's his computer.

Yes I know. That was the problem with my earlier patches.

The only reason the check is there at all is because background_ratio >
dirty_ratio has never been even tested, and could explode, and I don't want
to have to test and support it.  Plus if the admin is in the process of
setting both tunables there might be a transient period of time when
they're in a bad state.

That's all!  Please, just pretend the code isn't there at all.  What the
admin sets, the admin gets, end of story.

No, it is not that code I am worried about, you're actually doing
this too (disregarding the admin's wishes):

         dirty_ratio = vm_dirty_ratio;
         if (dirty_ratio > unmapped_ratio / 2)
                 dirty_ratio = unmapped_ratio / 2;

         if (dirty_ratio < 5)
                 dirty_ratio = 5;


So if the admin wants a dirty_ratio of 40 and dirty_background_ratio of 10
then that's good, but I'm sure if they knew you're moving dirty_ratio to 10
here, they'd want something like 2 for the dirty_background_ratio.

I contend that the ratio between these two values is more important than
their absolue values -- especially considering one gets twiddled here.
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