Messages in this thread | | | Date | Tue, 19 Dec 2017 12:22:32 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] kfree_rcu() should use the new kfree_bulk() interface for freeing rcu structures |
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On Tue, Dec 19, 2017 at 11:56:30AM -0800, Rao Shoaib wrote: > On 12/19/2017 11:30 AM, Matthew Wilcox wrote: > >On Tue, Dec 19, 2017 at 09:52:27AM -0800, rao.shoaib@oracle.com wrote:
[ . . . ]
> >I've been doing a lot of thinking about this because I really want a > >way to kfree_rcu() an object without embedding a struct rcu_head in it. > >But I see no way to do that today; even if we have an external memory > >allocation to point to the object to be freed, we have to keep track of > >the grace periods. > I am not sure I understand. If you had external memory you can > easily do that. > I am exactly doing that, the only reason the RCU structure is needed > is to get the pointer to the object being freed.
This can be done as long as you are willing to either:
1. Occasionally have kfree_rcu() wait for a grace period.
2. Occasionally have kfree_rcu() allocate memory.
3. Keep the rcu_head, but use it only when you would otherwise have to accept the above two penalties. (The point of this is that tracking lists of memory waiting for a grace period using dense arrays improves cache locality.)
There might be others, and if you come up with one, please don't keep it a secret. The C++ standards committee insisted on an interface using option #2 above. (There is also an option to use their equivalent of an rcu_head.)
Thanx, Paul
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