From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx131.postini.com [74.125.245.131]) by kanga.kvack.org (Postfix) with SMTP id C31656B004D for ; Thu, 22 Dec 2011 11:04:11 -0500 (EST) Message-ID: <4EF35477.8090007@ah.jp.nec.com> Date: Thu, 22 Dec 2011 11:01:59 -0500 From: Naoya Horiguchi MIME-Version: 1.0 Subject: Re: [PATCH 2/4] thp: optimize away unnecessary page table locking References: <1324506228-18327-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1324506228-18327-3-git-send-email-n-horiguchi@ah.jp.nec.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hillf Danton Cc: linux-mm@kvack.org, Andrew Morton , David Rientjes , Andi Kleen , Wu Fengguang , Andrea Arcangeli , KOSAKI Motohiro (12/22/2011 8:04), Hillf Danton wrote: > On Thu, Dec 22, 2011 at 6:23 AM, Naoya Horiguchi > wrote: >> Currently when we check if we can handle thp as it is or we need to >> split it into regular sized pages, we hold page table lock prior to >> check whether a given pmd is mapping thp or not. Because of this, >> when it's not "huge pmd" we suffer from unnecessary lock/unlock overhead. >> To remove it, this patch introduces a optimized check function and >> replace several similar logics with it. >> >> Signed-off-by: Naoya Horiguchi >> Cc: David Rientjes >> --- >> fs/proc/task_mmu.c | 74 ++++++++++------------------ >> include/linux/huge_mm.h | 7 +++ >> mm/huge_memory.c | 124 ++++++++++++++++++++++------------------------ >> mm/mremap.c | 3 +- >> 4 files changed, 93 insertions(+), 115 deletions(-) >> > > [...] > >> >> +/* >> + * Returns 1 if a given pmd is mapping a thp and stable (not under splitting.) >> + * Returns 0 otherwise. Note that if it returns 1, this routine returns without >> + * unlocking page table locks. So callers must unlock them. >> + */ >> +int check_and_wait_split_huge_pmd(pmd_t *pmd, struct vm_area_struct *vma) >> +{ >> + if (!pmd_trans_huge(*pmd)) >> + return 0; >> + >> + spin_lock(&vma->vm_mm->page_table_lock); >> + if (likely(pmd_trans_huge(*pmd))) { >> + if (pmd_trans_splitting(*pmd)) { >> + spin_unlock(&vma->vm_mm->page_table_lock); >> + wait_split_huge_page(vma->anon_vma, pmd); > > return 0; yes? Oops. You are right. Thank you. >> + } else { >> + /* Thp mapped by 'pmd' is stable, so we can >> + * handle it as it is. */ >> + return 1; >> + } >> + } >> + spin_unlock(&vma->vm_mm->page_table_lock); >> + return 0; >> +} >> + -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org