2012/7/6 Christoph Lameter <cl@xxxxxxxxx>: > On Fri, 6 Jul 2012, JoonSoo Kim wrote: > >> For example, >> When we try to free object A at cpu 1, another process try to free >> object B at cpu 2 at the same time. >> object A, B is in same slab, and this slab is in full list. >> >> CPU 1 CPU 2 >> prior = page->freelist; prior = page->freelist >> .... ... >> new.inuse--; new.inuse--; >> taking lock try to take the lock, but failed, so >> spinning... >> free success spinning... >> add_partial >> release lock taking lock >> fail cmpxchg_double_slab >> retry >> currently, we don't need lock >> >> At CPU2, we don't need lock anymore, because this slab already in partial list. > > For that scenario we could also simply do a trylock there and redo > the loop if we fail. But still what guarantees that another process will > not modify the page struct between fetching the data and a successful > trylock? I'm not familiar with English, so take my ability to understand into consideration. we don't need guarantees that another process will not modify the page struct between fetching the data and a successful trylock. As I understand, do u ask below scenario? CPU A CPU B lock cmpxchg fail retry unlock ... modify page strcut ... cmpxchg~~ In this case, cmpxchg will fail and just redo the loop. If we need the lock again during redo, re-take the lock. But I think this is not common case. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>