Re: new OOM heuristic failure (was: Re: VM: qsbench)

Lorenzo Allegrucci
2001-11-01T21:57:29Z

At 22.08 01/11/01 +0100, you wrote:
>> At 15.44 01/11/01 +0100, Stephan von Krawczynski wrote:
>> >On Wed, 31 Oct 2001 22:31:40 +0100 Lorenzo Allegrucci
><lenstra@tiscalinet.it>
>> >wrote:
>> >
>> >> Linus,
>> >>
>> >> your patch seems to help one case out of three.
>> >> (even though I have not any meaningful statistical data)
>> >
>> >Hm, I will not say that I expected that :-), he knows by far more
>than me.
>> >But can you try my patch below in addition or comparison to linus'
>?
>> >Give me a hint what happens.
>>
>> Well, your patch works but it hurts performance :(
>>
>> lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
>> 71.500u 1.790s 2:29.18 49.1% 0+0k 0+0io 18498pf+0w
>> lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
>> 71.460u 1.990s 2:26.87 50.0% 0+0k 0+0io 18257pf+0w
>> lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
>> 71.220u 2.200s 2:26.82 50.0% 0+0k 0+0io 18326pf+0w
>> 0:55 kswapd
>>
>> Linux-2.4.14-pre5:
>> lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
>> 70.340u 3.450s 2:13.62 55.2% 0+0k 0+0io 16829pf+0w
>> lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
>> 70.590u 2.940s 2:15.48 54.2% 0+0k 0+0io 17182pf+0w
>> lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
>> 70.140u 3.480s 2:14.66 54.6% 0+0k 0+0io 17122pf+0w
>> 0:01 kswapd
>
>Hello Lorenzo,
>
>to be honest: I expected that. The patch according to my knowledge
>fixes a "definition hole" in the shrink_cache algorithm. I tend to say
>it is the right thing to do it this way, but I am sure it is not as
>fast as immediate exit to swap. It would be interesting to know if it
>does hurt performance in not-near-oom environment. I'd say Andrea or
>Linus might know that, or you can try, of course :-)

400M of swap now (from 200M), Linux-2.4.14-pre6 + your vmscan-patch:

lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
71.320u 2.260s 2:28.92 49.4% 0+0k 0+0io 18755pf+0w
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
71.330u 2.120s 2:28.40 49.4% 0+0k 0+0io 18838pf+0w
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
71.880u 2.100s 2:28.31 49.8% 0+0k 0+0io 18646pf+0w
0:56 kswapd

qsbench vsize is just 343M, definitely not-near-oom environment :)

>Anyway may I beg you to post my patch and your answer to the list,
>because I currently cannot do it (I am not in office right now, but on
>a web-terminal somewhere in the outbacks ;-). I have neither patch at
>hand nor am I able to attach it with this mailer...
>
>Thanks,
>Stephan

your vmscan-patch:

--- linux-orig/mm/vmscan.c Wed Oct 31 12:32:11 2001
+++ linux/mm/vmscan.c Thu Nov 1 15:38:13 2001
@@ -469,16 +469,10 @@
spin_unlock(&pagecache_lock);
UnlockPage(page);
page_mapped:
- if (--max_mapped >= 0)
- continue;
+ if (max_mapped > 0)
+ max_mapped--;
+ continue;

- /*
- * Alert! We've found too many mapped pages on the
- * inactive list, so we start swapping out now!
- */
- spin_unlock(&pagemap_lru_lock);
- swap_out(priority, gfp_mask, classzone);
- return nr_pages;
}

/*
@@ -514,6 +508,14 @@
break;
}
spin_unlock(&pagemap_lru_lock);
+
+ /*
+ * Alert! We've found too many mapped pages on the
+ * inactive list, so we start swapping out - delayed!
+ * -skraw
+ */
+ if (max_mapped==0)
+ swap_out(priority, gfp_mask, classzone);

return nr_pages;
}

--
Lorenzo