Re: [PATCH] slub: Don't throw away partial remote slabs if there is no local memory

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Wed, Feb 05, 2014 at 06:07:57PM -0800, Nishanth Aravamudan wrote:
> On 24.01.2014 [16:25:58 -0800], David Rientjes wrote:
> > On Fri, 24 Jan 2014, Nishanth Aravamudan wrote:
> > 
> > > Thank you for clarifying and providing  a test patch. I ran with this on
> > > the system showing the original problem, configured to have 15GB of
> > > memory.
> > > 
> > > With your patch after boot:
> > > 
> > > MemTotal:       15604736 kB
> > > MemFree:         8768192 kB
> > > Slab:            3882560 kB
> > > SReclaimable:     105408 kB
> > > SUnreclaim:      3777152 kB
> > > 
> > > With Anton's patch after boot:
> > > 
> > > MemTotal:       15604736 kB
> > > MemFree:        11195008 kB
> > > Slab:            1427968 kB
> > > SReclaimable:     109184 kB
> > > SUnreclaim:      1318784 kB
> > > 
> > > 
> > > I know that's fairly unscientific, but the numbers are reproducible. 
> > > 
> > 
> > I don't think the goal of the discussion is to reduce the amount of slab 
> > allocated, but rather get the most local slab memory possible by use of 
> > kmalloc_node().  When a memoryless node is being passed to kmalloc_node(), 
> > which is probably cpu_to_node() for a cpu bound to a node without memory, 
> > my patch is allocating it on the most local node; Anton's patch is 
> > allocating it on whatever happened to be the cpu slab.
> > 
> > > > diff --git a/mm/slub.c b/mm/slub.c
> > > > --- a/mm/slub.c
> > > > +++ b/mm/slub.c
> > > > @@ -2278,10 +2278,14 @@ redo:
> > > > 
> > > >  	if (unlikely(!node_match(page, node))) {
> > > >  		stat(s, ALLOC_NODE_MISMATCH);
> > > > -		deactivate_slab(s, page, c->freelist);
> > > > -		c->page = NULL;
> > > > -		c->freelist = NULL;
> > > > -		goto new_slab;
> > > > +		if (unlikely(!node_present_pages(node)))
> > > > +			node = numa_mem_id();
> > > > +		if (!node_match(page, node)) {
> > > > +			deactivate_slab(s, page, c->freelist);
> > > > +			c->page = NULL;
> > > > +			c->freelist = NULL;
> > > > +			goto new_slab;
> > > > +		}
> > > 
> > > Semantically, and please correct me if I'm wrong, this patch is saying
> > > if we have a memoryless node, we expect the page's locality to be that
> > > of numa_mem_id(), and we still deactivate the slab if that isn't true.
> > > Just wanting to make sure I understand the intent.
> > > 
> > 
> > Yeah, the default policy should be to fallback to local memory if the node 
> > passed is memoryless.
> > 
> > > What I find odd is that there are only 2 nodes on this system, node 0
> > > (empty) and node 1. So won't numa_mem_id() always be 1? And every page
> > > should be coming from node 1 (thus node_match() should always be true?)
> > > 
> > 
> > The nice thing about slub is its debugging ability, what is 
> > /sys/kernel/slab/cache/objects showing in comparison between the two 
> > patches?
> 
> Ok, I finally got around to writing a script that compares the objects
> output from both kernels.
> 
> log1 is with CONFIG_HAVE_MEMORYLESS_NODES on, my kthread locality patch
> and Joonsoo's patch.
> 
> log2 is with CONFIG_HAVE_MEMORYLESS_NODES on, my kthread locality patch
> and Anton's patch.
> 
> slab                           objects    objects   percent
>                                log1       log2      change
> -----------------------------------------------------------
> :t-0000104                     71190      85680      20.353982 %
> UDP                            4352       3392       22.058824 %
> inode_cache                    54302      41923      22.796582 %
> fscache_cookie_jar             3276       2457       25.000000 %
> :t-0000896                     438        292        33.333333 %
> :t-0000080                     310401     195323     37.073978 %
> ext4_inode_cache               335        201        40.000000 %
> :t-0000192                     89408      128898     44.168307 %
> :t-0000184                     151300     81880      45.882353 %
> :t-0000512                     49698      73648      48.191074 %
> :at-0000192                    242867     120948     50.199904 %
> xfs_inode                      34350      15221      55.688501 %
> :t-0016384                     11005      17257      56.810541 %
> proc_inode_cache               103868     34717      66.575846 %
> tw_sock_TCP                    768        256        66.666667 %
> :t-0004096                     15240      25672      68.451444 %
> nfs_inode_cache                1008       315        68.750000 %
> :t-0001024                     14528      24720      70.154185 %
> :t-0032768                     655        1312       100.305344%
> :t-0002048                     14242      30720      115.700042%
> :t-0000640                     1020       2550       150.000000%
> :t-0008192                     10005      27905      178.910545%
> 
> FWIW, the configuration of this LPAR has slightly changed. It is now configured
> for maximally 400 CPUs, of which 200 are present. The result is that even with
> Joonsoo's patch (log1 above), we OOM pretty easily and Anton's slab usage
> script reports:
> 
> slab                                   mem     objs    slabs
>                                       used   active   active
> ------------------------------------------------------------
> kmalloc-512                        1182 MB    2.03%  100.00%
> kmalloc-192                        1182 MB    1.38%  100.00%
> kmalloc-16384                       966 MB   17.66%  100.00%
> kmalloc-4096                        353 MB   15.92%  100.00%
> kmalloc-8192                        259 MB   27.28%  100.00%
> kmalloc-32768                       207 MB    9.86%  100.00%
> 
> In comparison (log2 above):
> 
> slab                                   mem     objs    slabs
>                                       used   active   active
> ------------------------------------------------------------
> kmalloc-16384                       273 MB   98.76%  100.00%
> kmalloc-8192                        225 MB   98.67%  100.00%
> pgtable-2^11                        114 MB  100.00%  100.00%
> pgtable-2^12                        109 MB  100.00%  100.00%
> kmalloc-4096                        104 MB   98.59%  100.00%
> 
> I appreciate all the help so far, if anyone has any ideas how best to
> proceed further, or what they'd like debugged more, I'm happy to get
> this fixed. We're hitting this on a couple of different systems and I'd
> like to find a good resolution to the problem.

Hello,

I have no memoryless system, so, to debug it, I need your help. :)
First, please let me know node information on your system.

I'm preparing 3 another patches which are nearly same with previous patch,
but slightly different approach. Could you test them on your system?
I will send them soon.

And I think that same problem exists if CONFIG_SLAB is enabled. Could you
confirm that?

And, could you confirm that your system's numa_mem_id() is properly set?
And, could you confirm that node_present_pages() test works properly?
And, with my patches, could you give me more information on slub stat?
For this, you need to enable CONFIG_SLUB_STATS. Then please send me all the
slub stat on /proc/sys/kernel/debug/slab.

Sorry for too many request.
If it bothers you too much, please ignore it :)

Thanks.

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