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Christoph Lameter wrote: > On Tue, 23 Jan 2007, Balbir Singh wrote: > >> When you unmap or map, you need to touch the pte entries and know the >> pages involved, so shouldn't be equivalent to a list_del and list_add >> for each page impacted by the map/unmap operation? > > When you unmap and map you must currently get exclusive access to the > cachelines of the pte and the cacheline of the page struct. If we use a > list_move on page->lru then we have would have to update pointers in up > to 4 other page structs. Thus we need exclusive access to 4 additional > cachelines. This triples the number of cachelines touched. Instead of 2 > cachelines we need 6. > > Yes, good point, I see what you mean in terms of impact. But the trade off could come from shrink_active_list() which does list_del(&page->lru) if (!reclaim_mapped && other_conditions) list_add(&page->lru, &l_active); ... In the case mentioned above, we would triple the cachlines when an area is mapped/unmapped (which might be acceptable since it is a state change for the page ;) ). In the trade-off I mentioned, it would happen everytime reclaim is invoked and it has nothing to do with a page changing state. Did I miss something? -- Balbir Singh Linux Technology Center IBM, ISTL - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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