From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx162.postini.com [74.125.245.162]) by kanga.kvack.org (Postfix) with SMTP id 3C0996B008A for ; Tue, 20 Nov 2012 07:02:59 -0500 (EST) Received: by mail-bk0-f41.google.com with SMTP id jg9so2789106bkc.14 for ; Tue, 20 Nov 2012 04:02:57 -0800 (PST) Date: Tue, 20 Nov 2012 13:02:51 +0100 From: Ingo Molnar Subject: [PATCH] x86/mm: Don't flush the TLB on #WP pmd fixups Message-ID: <20121120120251.GA15742@gmail.com> References: <1353291284-2998-1-git-send-email-mingo@kernel.org> <20121119162909.GL8218@suse.de> <20121120060014.GA14065@gmail.com> <20121120074445.GA14539@gmail.com> <20121120090637.GA14873@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121120090637.GA14873@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Mel Gorman , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Peter Zijlstra , Paul Turner , Lee Schermerhorn , Christoph Lameter , Rik van Riel , Andrew Morton , Andrea Arcangeli , Linus Torvalds , Thomas Gleixner , Johannes Weiner , Hugh Dickins * Ingo Molnar wrote: > numa/core profile: > > 95.66% perf-1201.map [.] 0x00007fe4ad1c8fc7 > 1.70% libjvm.so [.] 0x0000000000381581 > 0.59% [vdso] [.] 0x0000000000000607 > 0.19% [kernel] [k] do_raw_spin_lock > 0.11% [kernel] [k] generic_smp_call_function_interrupt > 0.11% [kernel] [k] timekeeping_get_ns.constprop.7 > 0.08% [kernel] [k] ktime_get > 0.06% [kernel] [k] get_cycles > 0.05% [kernel] [k] __native_flush_tlb > 0.05% [kernel] [k] rep_nop > 0.04% perf [.] add_hist_entry.isra.9 > 0.04% [kernel] [k] rcu_check_callbacks > 0.04% [kernel] [k] ktime_get_update_offsets > 0.04% libc-2.15.so [.] __strcmp_sse2 > > No page fault overhead (see the page fault rate further below) > - the NUMA scanning overhead shows up only through some mild > TLB flush activity (which I'll fix btw). The patch attached below should get rid of that mild TLB flushing activity as well. Thanks, Ingo ---------------------------> Subject: x86/mm: Don't flush the TLB on #WP pmd fixups From: Ingo Molnar Date: Tue Nov 20 14:46:34 CET 2012 If we have a write protection #PF and fix up the pmd then the hugetlb code [the only user of pmdp_set_access_flags], in its do_huge_pmd_wp_page() page fault resolution function calls pmdp_set_access_flags() to mark the pmd permissive again, and flushes the TLB. This TLB flush is unnecessary: a flush on #PF is guaranteed on most (all?) x86 CPUs, and even in the worst-case we'll generate a spurious fault. So remove it. Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Cc: Andrea Arcangeli Cc: Hugh Dickins Signed-off-by: Ingo Molnar --- arch/x86/mm/pgtable.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) Index: linux/arch/x86/mm/pgtable.c =================================================================== --- linux.orig/arch/x86/mm/pgtable.c +++ linux/arch/x86/mm/pgtable.c @@ -334,7 +334,12 @@ int pmdp_set_access_flags(struct vm_area if (changed && dirty) { *pmdp = entry; pmd_update_defer(vma->vm_mm, address, pmdp); - flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE); + /* + * We had a write-protection fault here and changed the pmd + * to to more permissive. No need to flush the TLB for that, + * #PF is architecturally guaranteed to do that and in the + * worst-case we'll generate a spurious fault. + */ } return changed; -- 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