Re: pressuring dirty pages (2.3.99-pre6)

Rik van Riel
2000-04-24T22:42:12Z

On Mon, 24 Apr 2000, Stephen C. Tweedie wrote:
> On Mon, Apr 24, 2000 at 04:54:38PM -0300, Rik van Riel wrote:
> >
> > I've been trying to fix the VM balance for a week or so now,
> > and things are mostly fixed except for one situation.
> >
> > If there is a *heavy* write going on and the data is in the
> > page cache only .. ie. no buffer heads available, then the
> > page cache will grow almost without bounds and kswapd and
> > the rest of the system will basically spin in shrink_mmap()...
>
> shrink_mmap is the problem then -- it should be giving up sooner
> and letting try_to_swap_out() deal with the pages. mmap()ed
> dirty pages can only be freed through swapper activity, not via
> shrink_mmap().

That will not work. The problem isn't that kswapd eats cpu,
but the problem is that the dirty pages completely dominate
physical memory.

I've tried the "giving up earlier" option in shrink_mmap(),
but that leads to memory filling up just as badly and giving
us the same kind of trouble.

I guess what we want is the kind of callback that we do in
the direction of the buffer cache, using something like the
bdflush wakeup call done in try_to_free_buffers() ...

Maybe a "special" return value from shrink_mmap() telling
do_try_to_free_pages() to run swap_out() unconditionally
after this succesful shrink_mmap() call? Maybe even with
severity levels?

Eg. more calls to swap_out() if we encountered a lot of
dirty pages in shrink_mmap() ???

regards,

Rik
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