On Fri, Jun 08, 2012 at 02:43:58PM -0700, Linus Torvalds wrote: > On Fri, Jun 8, 2012 at 2:28 PM, Kirill A. Shutemov > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > > > > There's no reason to call rcu_barrier() on every deactivate_locked_super(). > > We only need to make sure that all delayed rcu free inodes are flushed > > before we destroy related cache. > > > > Removing rcu_barrier() from deactivate_locked_super() affects some > > fas paths. E.g. on my machine exit_group() of a last process in IPC > > namespace takes 0.07538s. rcu_barrier() takes 0.05188s of that time. > > I think we should just delete it. > > kmem_cache_destroy() (at least for SLUB) already has: > > if (s->flags & SLAB_DESTROY_BY_RCU) > rcu_barrier(); > > in it. But I think it's too late - it gets called *after* we do > kmem_cache_close(), and I get the feeling that we should do it before. > > Shouldn't that be sufficient? And if other slab allocators don't have > this, we should add it to them too. > > Hmm? When I tried SLAB_DESTROY_BY_RCU I've got problem: [ 36.687999] Pid: 3455, comm: rmmod Not tainted 3.5.0-rc1-00130-g48d212a-dirty #40 [ 36.688001] Call Trace: [ 36.688012] [<ffffffff8113367a>] slab_err+0xaa/0xd0 [ 36.688020] [<ffffffff8113515a>] ? __kmalloc+0x10a/0x110 [ 36.688026] [<ffffffff8113647d>] kmem_cache_destroy+0x1dd/0x420 [ 36.688056] [<ffffffffa00f0f25>] btrfs_destroy_cachep+0x15/0x60 [btrfs] [ 36.688076] [<ffffffffa013cac3>] exit_btrfs_fs+0x9/0x3a [btrfs] [ 36.688083] [<ffffffff810c324e>] sys_delete_module+0x16e/0x2f0 [ 36.688090] [<ffffffff8128cf29>] ? lockdep_sys_exit_thunk+0x35/0x67 [ 36.688097] [<ffffffff8161eba6>] system_call_fastpath+0x1a/0x1f [ 36.688111] Pid: 3455, comm: rmmod Not tainted 3.5.0-rc1-00130-g48d212a-dirty #40 [ 36.688114] Call Trace: [ 36.688119] [<ffffffff811365ee>] kmem_cache_destroy+0x34e/0x420 [ 36.688143] [<ffffffffa00f0f25>] btrfs_destroy_cachep+0x15/0x60 [btrfs] [ 36.688162] [<ffffffffa013cac3>] exit_btrfs_fs+0x9/0x3a [btrfs] [ 36.688168] [<ffffffff810c324e>] sys_delete_module+0x16e/0x2f0 [ 36.688174] [<ffffffff8128cf29>] ? lockdep_sys_exit_thunk+0x35/0x67 [ 36.688179] [<ffffffff8161eba6>] system_call_fastpath+0x1a/0x1f IIUC, moving rcu_barrier() up should help, but I can't say that I fully understand SLAB_DESTROY_BY_RCU semantics. -- Kirill A. Shutemov
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