Messages in this thread Patch in this message | | | Date | Wed, 19 Oct 2005 09:52:55 +0200 | From | Andrea Arcangeli <> | Subject | [PATCH] .text page fault SMP scalability optimization |
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We had a problem on ppc64 where with more than 4 threads a large system wouldn't scale well while faulting in the .text (most of the time was spent in the kernel despite it was an userland compute intensive app). The reason is the useless overwrite of the same pte from all cpu.
I fixed it this way (verified on an older kernel but the forward port is almost identical). This will benefit all archs not just ppc64.
Thanks.
From: Andrea Arcangeli <andrea@suse.de> Subject: make the .text parallel fault from multiple threads scale in smp
Signed-off-by: Andrea Arcangeli <andrea@suse.de>
memory.c | 12 +++++++----- 1 files changed, 7 insertions(+), 5 deletions(-)
Index: linux-2.6/mm/memory.c --- linux-2.6/mm/memory.c.~1~ 2005-09-21 17:38:48.000000000 +0200 +++ linux-2.6/mm/memory.c 2005-10-18 14:20:25.000000000 +0200 @@ -2000,7 +2000,7 @@ static inline int handle_pte_fault(struc struct vm_area_struct * vma, unsigned long address, int write_access, pte_t *pte, pmd_t *pmd) { - pte_t entry; + pte_t entry, young_entry; entry = *pte; if (!pte_present(entry)) { @@ -2021,10 +2021,12 @@ static inline int handle_pte_fault(struc return do_wp_page(mm, vma, address, pte, pmd, entry); entry = pte_mkdirty(entry); } - entry = pte_mkyoung(entry); - ptep_set_access_flags(vma, address, pte, entry, write_access); - update_mmu_cache(vma, address, entry); - lazy_mmu_prot_update(entry); + young_entry = pte_mkyoung(entry); + if (!pte_same(young_entry, entry)) { + ptep_set_access_flags(vma, address, pte, young_entry, write_access); + update_mmu_cache(vma, address, young_entry); + lazy_mmu_prot_update(young_entry); + } pte_unmap(pte); spin_unlock(&mm->page_table_lock); return VM_FAULT_MINOR; - 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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