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On a large SMP system with many CPUs, the global pool_lock may become a performance bottleneck as all the CPUs that need to allocate or free debug objects have to take the lock. That can sometimes cause soft lockups like: NMI watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [rcuos/1:21] ... RIP: 0010:[<ffffffff817c216b>] [<ffffffff817c216b>] _raw_spin_unlock_irqrestore+0x3b/0x60 ... Call Trace: [<ffffffff813f40d1>] free_object+0x81/0xb0 [<ffffffff813f4f33>] debug_check_no_obj_freed+0x193/0x220 [<ffffffff81101a59>] ? trace_hardirqs_on_caller+0xf9/0x1c0 [<ffffffff81284996>] ? file_free_rcu+0x36/0x60 [<ffffffff81251712>] kmem_cache_free+0xd2/0x380 [<ffffffff81284960>] ? fput+0x90/0x90 [<ffffffff81284996>] file_free_rcu+0x36/0x60 [<ffffffff81124c23>] rcu_nocb_kthread+0x1b3/0x550 [<ffffffff81124b71>] ? rcu_nocb_kthread+0x101/0x550 [<ffffffff81124a70>] ? sync_exp_work_done.constprop.63+0x50/0x50 [<ffffffff810c59d1>] kthread+0x101/0x120 [<ffffffff81101a59>] ? trace_hardirqs_on_caller+0xf9/0x1c0 [<ffffffff817c2d32>] ret_from_fork+0x22/0x50 To reduce the amount of contention on the pool_lock, the actual kmem_cache_free() of the debug objects will be delayed if the pool_lock is busy. This will temporarily increase the amount of free objects available at the free pool when the system is busy. As a result, the number of kmem_cache allocation and freeing is reduced. To further reduce the lock operations free debug objects in batches of four. Signed-off-by: Waiman Long <longman@redhat.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Du Changbin" <changbin.du@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jan Stancek <jstancek@redhat.com> Link: http://lkml.kernel.org/r/1483647425-4135-4-git-send-email-longman@redhat.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.