On 11/06/2012 04:14 AM, Mel Gorman wrote:
Note: Based on "mm/mpol: Use special PROT_NONE to migrate pages" but sufficiently different that the signed-off-bys were dropped Combine our previous _PAGE_NUMA, mpol_misplaced and migrate_misplaced_page() pieces into an effective migrate on fault scheme. Note that (on x86) we rely on PROT_NONE pages being !present and avoid the TLB flush from try_to_unmap(TTU_MIGRATION). This greatly improves the page-migration performance. Based-on-work-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
page = vm_normal_page(vma, addr, pte); BUG_ON(!page); + + get_page(page); + current_nid = page_to_nid(page); + target_nid = mpol_misplaced(page, vma, addr); + if (target_nid == -1) + goto clear_pmdnuma; + + pte_unmap_unlock(ptep, ptl); + migrate_misplaced_page(page, target_nid); + page = NULL; + + ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); + if (!pte_same(*ptep, pte)) + goto out_unlock; +
I see you tried to avoid the extraneous TLB flush from inside migrate_misplaced_page. However, try_to_unmap_one calls ptep_clear_flush, which will currently still result in a remote TLB flush for a _PAGE_NUMA pte, despite the pte not being accessible for memory accesses (_PAGE_PRESENT not set). Furthermore, if migrate_misplaced_page moved the page, the !pte_same check will return false, and you will get a double fault. I wonder if migrate_misplaced_page should return a struct page* or a pfn, so we can compute what "pte" _should_ be, corrected for the new pfn, feed that value to pte_same, and then avoid the double fault? Also, we may want the change for ptep_clear_flush that avoids flushing remote TLBs for a pte without the _PAGE_PRESENT bit set. -- 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>