Messages in this thread | | | Date | Sat, 07 Jan 2006 12:09:29 -0600 | From | Dave McCracken <> | Subject | Re: [PATCH/RFC] Shared page tables |
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--On Saturday, January 07, 2006 13:25:34 +0100 Heiko Carstens <heiko.carstens@de.ibm.com> wrote:
>> The primary purpose of sharing page tables is improved performance for >> large applications that share big memory areas between multiple >> processes. It eliminates the redundant page tables and significantly >> reduces the number of minor page faults. Tests show significant >> performance improvement for large database applications, including those >> using large pages. There is no measurable performance degradation for >> small processes. > > Tried to get this running with CONFIG_PTSHARE and CONFIG_PTSHARE_PTE on > s390x. Unfortunately it crashed on boot, because pt_share_pte > returned a broken pte pointer:
The patch as submitted only works on i386 and x86_64. Sorry.
>> +pte_t *pt_share_pte(struct vm_area_struct *vma, unsigned long address, >> pmd_t *pmd, + ... >> + pmd_val(spmde) = 0; >> + ... >> + if (pmd_present(spmde)) { > > This is wrong. A pmd_val of 0 will make pmd_present return true on s390x > which is not what you want. > Should be pmd_clear(&spmde). > >> +pmd_t *pt_share_pmd(struct vm_area_struct *vma, unsigned long address, >> pud_t *pud, + ... >> + pud_val(spude) = 0; > > Should be pud_clear, I guess :)
Yes, you're right. pmd_clear() and pud_clear() would be more portable. I'll make that change.
Dave McCracken
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