Re: [PATCH] mm: meminit: Finish initialisation of struct pages before basic setup

[Waiman Long]

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 That patch was superceded by "mm: meminit: finish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.

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.

Cheers,
Longman

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