From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx143.postini.com [74.125.245.143]) by kanga.kvack.org (Postfix) with SMTP id DFD776B0031 for ; Thu, 5 Sep 2013 11:23:28 -0400 (EDT) Date: Thu, 05 Sep 2013 11:23:08 -0400 From: Naoya Horiguchi Message-ID: <1378394588-k8upbl1n-mutt-n-horiguchi@ah.jp.nec.com> In-Reply-To: <87d2onwrs5.fsf@linux.vnet.ibm.com> References: <1377883120-5280-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1377883120-5280-2-git-send-email-n-horiguchi@ah.jp.nec.com> <87li3dvz3k.fsf@linux.vnet.ibm.com> <1378312330-afoa3r2y-mutt-n-horiguchi@ah.jp.nec.com> <87d2onwrs5.fsf@linux.vnet.ibm.com> Subject: Re: [PATCH 1/2] hugetlbfs: support split page table lock Mime-Version: 1.0 Content-Type: text/plain; charset=iso-2022-jp Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, Andrew Morton , Mel Gorman , Andi Kleen , Michal Hocko , KOSAKI Motohiro , Rik van Riel , Andrea Arcangeli , kirill.shutemov@linux.intel.com, Alex Thorlton , linux-kernel@vger.kernel.org On Thu, Sep 05, 2013 at 02:48:18PM +0530, Aneesh Kumar K.V wrote: > Naoya Horiguchi writes: > > > Hi Aneesh, > > > > On Wed, Sep 04, 2013 at 12:43:19PM +0530, Aneesh Kumar K.V wrote: > >> Naoya Horiguchi writes: > >> > >> > Currently all of page table handling by hugetlbfs code are done under > >> > mm->page_table_lock. So when a process have many threads and they heavily > >> > access to the memory, lock contention happens and impacts the performance. > >> > > >> > This patch makes hugepage support split page table lock so that we use > >> > page->ptl of the leaf node of page table tree which is pte for normal pages > >> > but can be pmd and/or pud for hugepages of some architectures. > >> > > >> > ChangeLog v2: > >> > - add split ptl on other archs missed in v1 > >> > > >> > Signed-off-by: Naoya Horiguchi > >> > --- > >> > arch/powerpc/mm/hugetlbpage.c | 6 ++- > >> > arch/tile/mm/hugetlbpage.c | 6 ++- > >> > include/linux/hugetlb.h | 20 ++++++++++ > >> > mm/hugetlb.c | 92 ++++++++++++++++++++++++++----------------- > >> > mm/mempolicy.c | 5 ++- > >> > mm/migrate.c | 4 +- > >> > mm/rmap.c | 2 +- > >> > 7 files changed, 90 insertions(+), 45 deletions(-) > >> > > >> > diff --git v3.11-rc3.orig/arch/powerpc/mm/hugetlbpage.c v3.11-rc3/arch/powerpc/mm/hugetlbpage.c > >> > index d67db4b..7e56cb7 100644 > >> > --- v3.11-rc3.orig/arch/powerpc/mm/hugetlbpage.c > >> > +++ v3.11-rc3/arch/powerpc/mm/hugetlbpage.c > >> > @@ -124,6 +124,7 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp, > >> > { > >> > struct kmem_cache *cachep; > >> > pte_t *new; > >> > + spinlock_t *ptl; > >> > > >> > #ifdef CONFIG_PPC_FSL_BOOK3E > >> > int i; > >> > @@ -141,7 +142,8 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp, > >> > if (! new) > >> > return -ENOMEM; > >> > > >> > - spin_lock(&mm->page_table_lock); > >> > + ptl = huge_pte_lockptr(mm, new); > >> > + spin_lock(ptl); > >> > >> > >> Are you sure we can do that for ppc ? > >> new = kmem_cache_zalloc(cachep, GFP_KERNEL|__GFP_REPEAT); > > > > Ah, thanks. new is not a pointer to one full page occupied by page > > table entries, so trying to use struct page of it is totally wrong. > > > >> The page for new(pte_t) could be shared right ? which mean a deadlock ? > > > > Yes, that's disastrous. > > > >> May be you should do it at the pmd level itself for ppc > > The pgd page also cannot be used because pgd also comes from kmem > cache. > > > > > Yes, that's possible, but I simply drop the changes in __hugepte_alloc() > > for now because this lock seems to protect us from the race between concurrent > > calls of __hugepte_alloc(), not between allocation and read/write access. > > Split ptl is used to avoid race between read/write accesses, so I think > > that using different types of locks here is not dangerous. > > # I guess that that's why we now use mm->page_table_lock for __pte_alloc() > > # and its family even if USE_SPLIT_PTLOCKS is true. > > A simpler approach could be to make huge_pte_lockptr arch > specific and leave it as mm->page_table_lock for ppc OK, I'll do this. Thanks, Naoya -- 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