From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 07 Jan 2006 12:09:29 -0600 From: Dave McCracken Subject: Re: [PATCH/RFC] Shared page tables Message-ID: <2796BAF66E63B415FF1929B8@[10.1.1.4]> In-Reply-To: <20060107122534.GA20442@osiris.boeblingen.de.ibm.com> References: <20060107122534.GA20442@osiris.boeblingen.de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: Heiko Carstens Cc: Hugh Dickins , Andrew Morton , Linux Kernel , Linux Memory Management List-ID: --On Saturday, January 07, 2006 13:25:34 +0100 Heiko Carstens 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org