On 03/29/2016 05:20 PM, Vlastimil Babka wrote: > On 03/28/2016 11:14 AM, Nikolay Borisov wrote: >> Hello, >> >> On kernel 4.4 I observe that the memory gets really fragmented fairly >> quickly. E.g. there are no order > 4 pages even after 2 days of uptime. >> This leads to certain data structures on XFS (in my case order 4/order 5 >> allocations) not being allocated and causes the server to stall. When >> this happens either someone has to log on the server and manually invoke >> the memory compaction or plain reboot the server. Before that the server >> was running with the exact same workload but with 3.12.52 kernel and no >> such issue were observed. That is - memory was fragmented but allocation >> didn't fail, maybe alloc_pages_direct_compact was doing a better job? >> >> FYI the allocation is performed with GFP_KERNEL | GFP_NOFS > > GFP_NOFS is indeed excluded from memory compaction in the allocation > context (i.e. direct compaction). > >> Manual compaction usually does the job, however I'm wondering why isn't >> invoking __alloc_pages_direct_compact from within __alloc_pages_nodemask >> satisfying the request if manual compaction would do the job. Is there a >> difference in the efficiency of manually invoking memory compaction and >> the one invoked from the page allocator path? > > Manual compaction via /proc is known to be safe in not holding any locks > that XFS might be holding. Compaction relies on page migration and IIRC > some filesystems cannot migrate dirty pages unless there's writeback, > and if that writeback called back to xfs, it would be a deadlock. > However, we could investigate if the async compaction would be safe. > > In any case, such high-order allocations should always have an order-0 > fallback. You're suggesting there's an infinite loop around the > allocation attempt instead? Do you have the full backtrace? Yes, here is a full backtrace: loop0 D ffff881fe081f038 0 15174 2 0x00000000 ffff881fe081f038 ffff883ff29fa700 ffff881fecb70d00 ffff88407fffae00 0000000000000000 0000000502404240 ffffffff81e30d60 0000000000000000 0000000000000000 ffff881f00000003 0000000000000282 ffff883f00000000 Call Trace: [<ffffffff8163ac01>] ? _raw_spin_lock_irqsave+0x21/0x60 [<ffffffff81636fd7>] schedule+0x47/0x90 [<ffffffff81639f03>] schedule_timeout+0x113/0x1e0 [<ffffffff810ac580>] ? lock_timer_base+0x80/0x80 [<ffffffff816363d4>] io_schedule_timeout+0xa4/0x110 [<ffffffff8114aadf>] congestion_wait+0x7f/0x130 [<ffffffff810939e0>] ? woken_wake_function+0x20/0x20 [<ffffffffa0283bac>] kmem_alloc+0x8c/0x120 [xfs] [<ffffffff81181751>] ? __kmalloc+0x121/0x250 [<ffffffffa0283c73>] kmem_realloc+0x33/0x80 [xfs] [<ffffffffa02546cd>] xfs_iext_realloc_indirect+0x3d/0x60 [xfs] [<ffffffffa02548cf>] xfs_iext_irec_new+0x3f/0xf0 [xfs] [<ffffffffa0254c0d>] xfs_iext_add_indirect_multi+0x14d/0x210 [xfs] [<ffffffffa02554b5>] xfs_iext_add+0xc5/0x230 [xfs] [<ffffffff8112b5c5>] ? mempool_alloc_slab+0x15/0x20 [<ffffffffa0256269>] xfs_iext_insert+0x59/0x110 [xfs] [<ffffffffa0230928>] ? xfs_bmap_add_extent_hole_delay+0xd8/0x740 [xfs] [<ffffffffa0230928>] xfs_bmap_add_extent_hole_delay+0xd8/0x740 [xfs] [<ffffffff8112b5c5>] ? mempool_alloc_slab+0x15/0x20 [<ffffffff8112b725>] ? mempool_alloc+0x65/0x180 [<ffffffffa02543d8>] ? xfs_iext_get_ext+0x38/0x70 [xfs] [<ffffffffa0254e8d>] ? xfs_iext_bno_to_ext+0xed/0x150 [xfs] [<ffffffffa02311b5>] xfs_bmapi_reserve_delalloc+0x225/0x250 [xfs] [<ffffffffa023131e>] xfs_bmapi_delay+0x13e/0x290 [xfs] [<ffffffffa02730ad>] xfs_iomap_write_delay+0x17d/0x300 [xfs] [<ffffffffa022e434>] ? xfs_bmapi_read+0x114/0x330 [xfs] [<ffffffffa025ddc5>] __xfs_get_blocks+0x585/0xa90 [xfs] [<ffffffff81324b53>] ? __percpu_counter_add+0x63/0x80 [<ffffffff811374cd>] ? account_page_dirtied+0xed/0x1b0 [<ffffffff811cfc59>] ? alloc_buffer_head+0x49/0x60 [<ffffffff811d07c0>] ? alloc_page_buffers+0x60/0xb0 [<ffffffff811d13e5>] ? create_empty_buffers+0x45/0xc0 [<ffffffffa025e324>] xfs_get_blocks+0x14/0x20 [xfs] [<ffffffff811d34e2>] __block_write_begin+0x1c2/0x580 [<ffffffffa025e310>] ? xfs_get_blocks_direct+0x20/0x20 [xfs] [<ffffffffa025bbb1>] xfs_vm_write_begin+0x61/0xf0 [xfs] [<ffffffff81127e50>] generic_perform_write+0xd0/0x1f0 [<ffffffffa026a341>] xfs_file_buffered_aio_write+0xe1/0x240 [xfs] [<ffffffff812e16d2>] ? bt_clear_tag+0xb2/0xd0 [<ffffffffa026ab87>] xfs_file_write_iter+0x167/0x170 [xfs] [<ffffffff81199d76>] vfs_iter_write+0x76/0xa0 [<ffffffffa03fb735>] lo_write_bvec+0x65/0x100 [loop] [<ffffffffa03fd589>] loop_queue_work+0x689/0x924 [loop] [<ffffffff8163ba52>] ? retint_kernel+0x10/0x10 [<ffffffff81074d71>] kthread_worker_fn+0x61/0x1c0 [<ffffffff81074d10>] ? flush_kthread_work+0x120/0x120 [<ffffffff81074d10>] ? flush_kthread_work+0x120/0x120 [<ffffffff810744d7>] kthread+0xd7/0xf0 [<ffffffff8107d22e>] ? schedule_tail+0x1e/0xd0 [<ffffffff81074400>] ? kthread_freezable_should_stop+0x80/0x80 [<ffffffff8163b2af>] ret_from_fork+0x3f/0x70 [<ffffffff81074400>] ? kthread_freezable_should_stop+0x80/0x80 Basically on a very large sparse file the array which holds the extents that describe said file can grow fairly big. In this particular case it couldn't satisfy an order-5 allocation as evident from the following message from xfs: XFS: loop0(15174) possible memory allocation deadlock size 107168 in kmem_alloc (mode:0x2400240) This basically says "I cannot allocate 107 contiguous kb" And here is a discussion that ensued on xfs mailing list: http://oss.sgi.com/archives/xfs/2016-03/msg00447.html -- 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>