On Mon, May 09, 2011 at 01:16:20PM -0500, James Bottomley wrote: > On Fri, 2011-05-06 at 09:07 +0100, Mel Gorman wrote: > > On Fri, May 06, 2011 at 08:42:24AM +0100, Mel Gorman wrote: > > > 1. High-order allocations? You machine is using i915 and RPC, something > > > neither of my test machine uses. i915 is potentially a source for > > > high-order allocations. I'm attaching a perl script. Please run it as > > > ./watch-highorder.pl --output /tmp/highorders.txt > > > while you are running tar. When kswapd is running for about 30 > > > seconds, interrupt it with ctrl+c twice in quick succession and > > > post /tmp/highorders.txt > > > > > > > Attached this time :/ > > Here's the output (loaded with tar, evolution and firefox). The top > trace is different this time because your perl script perturbs the > system quite a bit. This was with your slub allocation fix applied. > I note that certain flags like __GFP_NO_KSWAPD are not recognised by tracing which might explain why they are missing from the script output. I regret the script perturbs the system quite a bit. It's possible it can be made better by filtering events but it's not high on the list of things to do. How does the output compare without the fix? I can't find a similar report in my inbox. Does the fix help the system when the perl script is not running? > 177 instances order=2 normal gfp_flags=GFP_NOFS|GFP_NOWARN|GFP_NORETRY|GFP_COMP|GFP_RECLAIMABLE| > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => alloc_pages_current+0xbe/0xd8 <ffffffff81105435> > => alloc_slab_page+0x1c/0x4d <ffffffff8110c5da> > => new_slab+0x50/0x199 <ffffffff8110dc24> > => __slab_alloc+0x24a/0x328 <ffffffff8146ab66> > => kmem_cache_alloc+0x77/0x105 <ffffffff8110e42c> > => radix_tree_preload+0x31/0x81 <ffffffff81229399> > => add_to_page_cache_locked+0x56/0x118 <ffffffff810d57d5> > Ouch. > 46 instances order=1 normal gfp_flags=GFP_KERNEL|GFP_NOWARN|GFP_NORETRY|GFP_COMP| > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => alloc_pages_current+0xbe/0xd8 <ffffffff81105435> > => alloc_slab_page+0x1c/0x4d <ffffffff8110c5da> > => new_slab+0x50/0x199 <ffffffff8110dc24> > => __slab_alloc+0x24a/0x328 <ffffffff8146ab66> > => kmem_cache_alloc+0x77/0x105 <ffffffff8110e42c> > => prepare_creds+0x26/0xae <ffffffff81074d4b> > => sys_faccessat+0x37/0x162 <ffffffff8111d255> > Less ouch, but still. > 252 instances order=2 normal gfp_flags=GFP_TEMPORARY|GFP_NOWARN|GFP_NORETRY|GFP_COMP| > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => alloc_pages_current+0xbe/0xd8 <ffffffff81105435> > => alloc_slab_page+0x1c/0x4d <ffffffff8110c5da> > => new_slab+0x50/0x199 <ffffffff8110dc24> > => __slab_alloc+0x24a/0x328 <ffffffff8146ab66> > => kmem_cache_alloc+0x77/0x105 <ffffffff8110e42c> > => radix_tree_preload+0x31/0x81 <ffffffff81229399> > => add_to_page_cache_locked+0x56/0x118 <ffffffff810d57d5> > Ouch again. > 593 instances order=3 normal gfp_flags=GFP_NOFS|GFP_NOWARN|GFP_NORETRY|GFP_COMP|GFP_RECLAIMABLE| > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => alloc_pages_current+0xbe/0xd8 <ffffffff81105435> > => alloc_slab_page+0x1c/0x4d <ffffffff8110c5da> > => new_slab+0x50/0x199 <ffffffff8110dc24> > => __slab_alloc+0x24a/0x328 <ffffffff8146ab66> > => kmem_cache_alloc+0x77/0x105 <ffffffff8110e42c> > => ext4_alloc_inode+0x1a/0x111 <ffffffff8119f498> > => alloc_inode+0x1d/0x78 <ffffffff811317e5> > Again, filesystem-related calls are hitting high-order paths quite a bit. > 781 instances order=2 normal gfp_flags=GFP_KERNEL|GFP_REPEAT|GFP_COMP > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => kmalloc_large_node+0x56/0x95 <ffffffff8146a55d> > => __kmalloc_node_track_caller+0x31/0x131 <ffffffff8110ff08> > => __alloc_skb+0x75/0x133 <ffffffff813b5e2c> > => sock_alloc_send_pskb+0xb4/0x2d7 <ffffffff813b238a> > => sock_alloc_send_skb+0x15/0x17 <ffffffff813b25c2> > => unix_stream_sendmsg+0x11e/0x2ec <ffffffff8143d217> > => __sock_sendmsg+0x69/0x76 <ffffffff813af778> > A number of network paths are also being hit although this is the worst. > 501 instances order=1 normal gfp_flags=GFP_KERNEL|GFP_NOWARN|GFP_NORETRY|GFP_COMP| > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => alloc_pages_current+0xbe/0xd8 <ffffffff81105435> > => alloc_slab_page+0x1c/0x4d <ffffffff8110c5da> > => new_slab+0x50/0x199 <ffffffff8110dc24> > => __slab_alloc+0x24a/0x328 <ffffffff8146ab66> > => kmem_cache_alloc+0x77/0x105 <ffffffff8110e42c> > => get_empty_filp+0x7a/0x141 <ffffffff8111f2d1> > => do_filp_open+0xe7/0x60a <ffffffff81129bcf> > More filesystem impairment. > 1370 instances order=1 normal gfp_flags=GFP_TEMPORARY|GFP_NOWARN|GFP_NORETRY|GFP_COMP| > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => alloc_pages_current+0xbe/0xd8 <ffffffff81105435> > => alloc_slab_page+0x1c/0x4d <ffffffff8110c5da> > => new_slab+0x50/0x199 <ffffffff8110dc24> > => __slab_alloc+0x24a/0x328 <ffffffff8146ab66> > => kmem_cache_alloc+0x77/0x105 <ffffffff8110e42c> > => d_alloc+0x26/0x18d <ffffffff8112e4c5> > => d_alloc_and_lookup+0x2c/0x6b <ffffffff81126d0e> > *cries* > 140358 instances order=1 normal gfp_flags=GFP_NOWARN|GFP_NORETRY|GFP_COMP|GFP_NOMEMALLOC| > => __alloc_pages_nodemask+0x737/0x772 <ffffffff810dc0bd> > => alloc_pages_current+0xbe/0xd8 <ffffffff81105435> > => alloc_slab_page+0x1c/0x4d <ffffffff8110c5da> > => new_slab+0x50/0x199 <ffffffff8110dc24> > => __slab_alloc+0x24a/0x328 <ffffffff8146ab66> > => kmem_cache_alloc+0x77/0x105 <ffffffff8110e42c> > => mempool_alloc_slab+0x15/0x17 <ffffffff810d6e81> > => mempool_alloc+0x68/0x116 <ffffffff810d70f6> Wonder which pool this is! It goes on. A number of filesystem and network paths are being hit with high-order allocs. i915 was a red herring, it's present but not in massive numbers. The filesystem, network and mempool allocations are likely to be kicking kswapd awake frequently and hurting overall system performance as a result. I really would like to hear if the fix makes a big difference or if we need to consider forcing SLUB high-order allocations bailing at the first sign of trouble (e.g. by masking out __GFP_WAIT in allocate_slab). Even with the fix applied, kswapd might be waking up less but processes will still be getting stalled in direct compaction and direct reclaim so it would still be jittery. > High-order normal allocations: 145450 > High-order atomic allocations: 927 > I bet a shiny penny that the high-order allocations for SLAB are lower than this -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
