On Tue, 3 Feb 2009, Eric Dumazet wrote: > Andrew Morton a écrit : > > On Mon, 2 Feb 2009 11:20:09 -0700 > > Jonathan Corbet <corbet@xxxxxxx> wrote: > > > >> Matt Mackall suggested converting epoll's ep_lock to a bitlock as a way of > >> saving space in struct file. This patch makes that change. > > > > hrm. bit_spin_lock() makes people upset (large penguiny people). iirc > > it doesn't have all the correct/well-understood memory/compiler > > ordering semantics which spinlocks have. And lockdep doesn't know about > > it. > > > > In a previous attempt (2005), I suggested using a single global lock. > > http://search.luky.org/linux-kernel.2005/msg50862.html > > Probably an array of hashed spinlocks would be more than enough. That could be done, although I'm not sure it's worth going that way to save 4 bytes. The effective saving rate is not even 4/sizeof(struct file) since struct file never comes alone, and when you allocate a struct file you always carry more allocations behind (at least for the cases where you tend to have a lot of them around, so size would matter). The add/remove path in epoll is not a super-hot one, so it could be done. I dunno how this change matter with the patchset though. - Davide
