--
Daniel J Blueman
Principal Software Engineer, Numascale
On Sat, May 23, 2015 at 1:14 AM, Waiman Long <waiman.long@xxxxxx> wrote:
On 05/22/2015 05:33 AM, Mel Gorman wrote:
On Fri, May 22, 2015 at 02:30:01PM +0800, Daniel J Blueman wrote:
On Thu, May 14, 2015 at 6:03 PM, Daniel J Blueman
<daniel@xxxxxxxxxxxxx> wrote:
On Thu, May 14, 2015 at 12:31 AM, Mel Gorman<mgorman@xxxxxxx>
wrote:
On Wed, May 13, 2015 at 10:53:33AM -0500, nzimmer wrote:
I am just noticed a hang on my largest box.
I can only reproduce with large core counts, if I turn down the
number of cpus it doesn't have an issue.
Odd. The number of core counts should make little a difference
as only
one CPU per node should be in use. Does sysrq+t give any
indication how
or where it is hanging?
I was seeing the same behaviour of 1000ms increasing to 5500ms
[1]; this suggests either lock contention or O(n) behaviour.
Nathan, can you check with this ordering of patches from Andrew's
cache [2]? I was getting hanging until I a found them all.
I'll follow up with timing data.
7TB over 216 NUMA nodes, 1728 cores, from kernel 4.0.4 load to
login:
1. 2086s with patches 01-19 [1]
2. 2026s adding "Take into account that large system caches scale
linearly with memory", which has:
min(2UL<< (30 - PAGE_SHIFT), (pgdat->node_spanned_pages>> 3));
3. 2442s fixing to:
max(2UL<< (30 - PAGE_SHIFT), (pgdat->node_spanned_pages>> 3));
4. 2064s adjusting minimum and shift to:
max(512UL<< (20 - PAGE_SHIFT), (pgdat->node_spanned_pages>> 8));
5. 1934s adjusting minimum and shift to:
max(128UL<< (20 - PAGE_SHIFT), (pgdat->node_spanned_pages>> 8));
6. 930s #5 with the non-temporal PMD init patch I had earlier
proposed (I'll pursue separately)
The scaling patch isn't in -mm.
That patch was superceded by "mm: meminit: finish
initialisation of struct pages before basic setup" and
"mm-meminit-finish-initialisation-of-struct-pages-before-basic-setup-fix"
so that's ok.
FWIW, I think you should still go ahead with the non-temporal
patches because
there is potential benefit there other than the initialisation. If
there
was an arch-optional implementation of a non-termporal clear then it
would
also be worth considering if __GFP_ZERO should use non-temporal
stores.
At a greater stretch it would be worth considering if kswapd freeing
should
zero pages to avoid a zero on the allocation side in the general
case as
it would be more generally useful and a stepping stone towards what
the
series "Sanitizing freed pages" attempts.
Good tip Mel; I'll take a look when time allows and get some data,
though I guess it'll only be a win where the clearing is on a different
node than the allocation.
I think the non-temporal patch benefits mainly AMD systems. I have
tried the patch on both DragonHawk and it actually made it boot up a
little bit slower. I think the Intel optimized "rep stosb"
instruction (used in memset) is performing well. I had done similar
test on zero page code and the performance gain was non-conclusive.
I suspect 'rep stosb' on modern Intel hardware can write whole
cachelines atomically, avoiding the RMW, or that the read part of the
RMW is optimally prefetched. Open-coding it just can't reach the same
level of pipeline saturation that the microcode can.
Daniel
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>