Messages in this thread | | | Date | Tue, 20 Nov 2007 13:36:58 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: [rfc 04/45] cpu alloc: Use in SLUB |
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On Tue, 20 Nov 2007, Mathieu Desnoyers wrote:
> > > > - __slab_free(s, page, x, addr, c->offset); > > > > + if (unlikely(page != __CPU_READ(c->page) || > > > > + __CPU_READ(c->node) < 0)) { > > > > + __slab_free(s, page, x, addr, __CPU_READ(c->offset)); > > > > > > And same question as above : what happens if we fail after executing the > > > __slab_free.. is it valid to do it twice ? > > > > __slab_free is always successful and will never cause a repeat of the > > loop. > > Then what happens if we are migrated between the end of __slab_free and > the CPU_CMPXCHG ? The cmpxchg would fail, and the __slab_free will be > done twice ?
Look at the control flow. The __slab_free can never be done twice.
{ freelist = __CPU_READ(c->freelist); barrier(); if (unlikely(page != __CPU_READ(c->page) || __CPU_READ(c->node) < 0)) { __slab_free(s, page, x, addr); break; ^^^^^^^ no redo of the loop possible.
} set_freepointer(s, object, freelist); } while (CPU_CMPXCHG(c->freelist, freelist, object) != freelist);
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