> On 27 Nov 1998, Zlatko Calusic wrote:
> > "Stephen C. Tweedie" <sct@redhat.com> writes:
> >
> > > The real problem seems to be that shrink_mmap() can fail for two
> > > completely separate reasons. First of all, we might fail to find a
> > > free page because all of the cache pages we find are recently
> > > referenced. Secondly, we might fail to find a cache page at all.
> >
> > Yesterday, I was trying to understand the very same problem you're
> > speaking of. Sometimes kswapd decides to swapout lots of things,
> > sometimes not.
> >
> > I applied your patch, but it didn't solve the problem.
> > To be honest, things are now even slightly worse. :(
>
> The 'fix' is to lower the borrow percentages for both
> the buffer cache and the page cache. If we don't do
> that (or abolish the percentages completely) kswapd
> doesn't have an incentive to switch from a succesful
> round of swap_out() -- which btw doesn't free any
> actual memory so kswapd just continues doing that --
> to shrink_mmap().
Yep, this is the conclusion of my experiments, too.
>
> Another thing we might want to try is inserting the
> following test in do_try_to_free_page():
>
> if (atomic_read(&nr_async_pages) >= pager_daemon.swap_cluster)
> state = 0;
>
> This will switch kswapd to shrink_mmap() when we have enough
> pages queued for efficient swap I/O. Of course this 'fix'
> decreases swap throughput so we might want to think up something
> more clever instead...
>
Exactly.
It is funny how we tried same things in order to find a solution. :)
I made the following change in do_try_to_free_page():
(writing from memory, notice the concept)
...
case 2:
>> swapouts++;
>> if (swapouts > pager_daemon.swap_cluster) {
>> swapouts = 0;
>> state = 3;
>> }
if (swap_out(i, gfp_mask))
return 1;
state = 3;
case 3:
shrink_dcache_memory(i, gfp_mask);
state = 0;
i--;
} while (i >= 0);
Unfortunately, this really killed swapout performance, so I dropped
the idea. Even letting swap_out do more passes, before changing state,
didn't feel good.
One other idea I had, was to replace (code at the very beginning of
do_try_to_free_page()):
if (buffer_over_borrow() || pgcache_over_borrow())
shrink_mmap(i, gfp_mask);
with:
if (buffer_over_borrow() || pgcache_over_borrow())
state = 0;
While this looks like a good idea, it in fact makes kswapd a CPU hog,
and also doesn't help performance, because it makes limits too hard,
and there's slight debalance.
I'll keep hacking... :)
-- Posted by Zlatko Calusic E-mail: <Zlatko.Calusic@CARNet.hr> --------------------------------------------------------------------- If you don't think women are explosive, drop one!- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/