Messages in this thread | | | Date | Fri, 6 Jul 2012 23:59:31 +0900 | Subject | Re: [PATCH 3/3] slub: release a lock if freeing object with a lock is failed in __slab_free() | From | JoonSoo Kim <> |
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2012/7/6 Christoph Lameter <cl@linux.com>: > 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.
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