RHEL 5.7 appears to hangs when vm.dirty_bytes and vm.dirty_ratio are lowered and a high I/O is applied.
Issue
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When vm.dirty_bytes and vm.dirty_ratio are lowered and a moderate to heavy IO operation is done, the system appears to hang e.g:
vm.dirty_bytes = 512000 vm.dirty_ratio = 0 -
Incomplete vmcore is generated by nfs in kdump.
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Following type of trace can be observed,
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. ls D ffff81000503eaa0 0 2937 2896 (NOTLB) ffff810008d17d98 0000000000000086 ffff81000c146620 ffff81000c146218 ffff81000898a460 0000000000000007 ffff81000be53860 ffff81000fc36100 0000012fb24ffad2 00000000000023c9 ffff81000be53a48 0000000108d17e48 Call Trace: [<ffffffff8000a851>] __link_path_walk+0xfa8/0xfd1 [<ffffffff80063c53>] __mutex_lock_slowpath+0x60/0x9b [<ffffffff80063c9d>] .text.lock.mutex+0xf/0x14 [<ffffffff886bf787>] :nfs:nfs_getattr+0x45/0xd9 [<ffffffff8003efd6>] vfs_lstat_fd+0x2f/0x47 [<ffffffff8002ad86>] sys_newlstat+0x19/0x31 [<ffffffff80038a15>] sys_getdents+0xaf/0xbd [<ffffffff8005dde9>] error_exit+0x0/0x84 [<ffffffff8005d116>] system_call+0x7e/0x83
Environment
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Red Hat Enterprise Linux 5.7 with VM writeback ratios lowered.
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A vmcore copy over NFS or heavy IO operation.
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