Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758593Ab3GZLVJ (ORCPT ); Fri, 26 Jul 2013 07:21:09 -0400 Received: from merlin.infradead.org ([205.233.59.134]:32902 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758206Ab3GZLVF (ORCPT ); Fri, 26 Jul 2013 07:21:05 -0400 Date: Fri, 26 Jul 2013 13:20:50 +0200 From: Peter Zijlstra To: Mel Gorman Cc: Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML Subject: Re: [PATCH 15/18] sched: Set preferred NUMA node based on number of private faults Message-ID: <20130726112050.GJ27075@twins.programming.kicks-ass.net> References: <1373901620-2021-1-git-send-email-mgorman@suse.de> <1373901620-2021-16-git-send-email-mgorman@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1373901620-2021-16-git-send-email-mgorman@suse.de> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3932 Lines: 106 On Mon, Jul 15, 2013 at 04:20:17PM +0100, Mel Gorman wrote: > diff --git a/mm/mprotect.c b/mm/mprotect.c > index cacc64a..04c9469 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -37,14 +37,15 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot) > > static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long addr, unsigned long end, pgprot_t newprot, > - int dirty_accountable, int prot_numa, bool *ret_all_same_node) > + int dirty_accountable, int prot_numa, bool *ret_all_same_nidpid) > { > struct mm_struct *mm = vma->vm_mm; > pte_t *pte, oldpte; > spinlock_t *ptl; > unsigned long pages = 0; > - bool all_same_node = true; > + bool all_same_nidpid = true; > int last_nid = -1; > + int last_pid = -1; > > pte = pte_offset_map_lock(mm, pmd, addr, &ptl); > arch_enter_lazy_mmu_mode(); > @@ -64,10 +65,17 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > page = vm_normal_page(vma, addr, oldpte); > if (page) { > int this_nid = page_to_nid(page); > + int nidpid = page_nidpid_last(page); > + int this_pid = nidpid_to_pid(nidpid); > + > if (last_nid == -1) > last_nid = this_nid; > - if (last_nid != this_nid) > - all_same_node = false; > + if (last_pid == -1) > + last_pid = this_pid; > + if (last_nid != this_nid || > + last_pid != this_pid) { > + all_same_nidpid = false; > + } At this point I would've expected something like: int nidpid = page_nidpid_last(page); int thisnid = nidpid_to_nid(nidpid); int thispid = nidpit_to_pid(nidpit); It seems 'weird' to mix the state like you did; is there a reason the above is incorrect? > > if (!pte_numa(oldpte)) { > ptent = pte_mknuma(ptent); > @@ -106,7 +114,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > arch_leave_lazy_mmu_mode(); > pte_unmap_unlock(pte - 1, ptl); > > - *ret_all_same_node = all_same_node; > + *ret_all_same_nidpid = all_same_nidpid; > return pages; > } > > @@ -133,7 +141,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, > pmd_t *pmd; > unsigned long next; > unsigned long pages = 0; > - bool all_same_node; > + bool all_same_nidpid; > > pmd = pmd_offset(pud, addr); > do { > @@ -151,7 +159,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, > if (pmd_none_or_clear_bad(pmd)) > continue; > pages += change_pte_range(vma, pmd, addr, next, newprot, > - dirty_accountable, prot_numa, &all_same_node); > + dirty_accountable, prot_numa, &all_same_nidpid); > > /* > * If we are changing protections for NUMA hinting faults then > @@ -159,7 +167,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, > * node. This allows a regular PMD to be handled as one fault > * and effectively batches the taking of the PTL > */ > - if (prot_numa && all_same_node) > + if (prot_numa && all_same_nidpid) > change_pmd_protnuma(vma->vm_mm, addr, pmd); > } while (pmd++, addr = next, addr != end); > Hurmph I just stumbled upon this PMD 'trick' and I'm not at all sure I like it. If an application would pre-fault/initialize its memory with the main thread we'll collapse it into a PMDs and forever thereafter (by virtue of do_pmd_numa_page()) they'll all stay the same. Resulting in PMD granularity. It seems possible that concurrent faults can break it up, but the window is tiny so I don't expect to actually see that happening. In any case, this thing needs comments; both here in mprotect and near do_pmu_numa_page(). -- 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/