From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756943Ab1D0OgK (ORCPT ); Wed, 27 Apr 2011 10:36:10 -0400 Received: from arkanian.console-pimps.org ([212.110.184.194]:37879 "EHLO arkanian.console-pimps.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754120Ab1D0OgJ (ORCPT ); Wed, 27 Apr 2011 10:36:09 -0400 From: Matt Fleming To: Dave Hansen Cc: Hugh Dickins , KAMEZAWA Hiroyuki , Andrew Morton , linux-mm@vger.kernel.org, linux-kernel@vger.kernel.org, Matt Fleming Subject: [PATCH] mm: Delete non-atomic mm counter implementation Date: Wed, 27 Apr 2011 15:36:05 +0100 Message-Id: <1303914965-868-1-git-send-email-matt@console-pimps.org> X-Mailer: git-send-email 1.7.4.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matt Fleming The problem with having two different types of counters is that developers adding new code need to keep in mind whether it's safe to use both the atomic and non-atomic implementations. For example, when adding new callers of the *_mm_counter() functions a developer needs to ensure that those paths are always executed with page_table_lock held, in case we're using the non-atomic implementation of mm counters. Hugh Dickins introduced the atomic mm counters in commit f412ac08c986 ("[PATCH] mm: fix rss and mmlist locking"). When asked why he left the non-atomic counters around he said, | The only reason was to avoid adding costly atomic operations into a | configuration that had no need for them there: the page_table_lock | sufficed. | | Certainly it would be simpler just to delete the non-atomic variant. | | And I think it's fair to say that any configuration on which we're | measuring performance to that degree (rather than "does it boot fast?" | type measurements), would already be going the split ptlocks route. Removing the non-atomic counters eases the maintenance burden because developers no longer have to mindful of the two implementations when using *_mm_counter(). Note that all architectures provide a means of atomically updating atomic_long_t variables, even if they have to revert to the generic spinlock implementation because they don't support 64-bit atomic instructions (see lib/atomic64.c). Signed-off-by: Matt Fleming --- Dave, you might want to take this into your pagetable counters series so that you only need to worry about atomic mm counters. include/linux/mm.h | 44 +++++++------------------------------------- include/linux/mm_types.h | 9 +++------ 2 files changed, 10 insertions(+), 43 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index dd87a78..ee64af2 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1034,65 +1034,35 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write, /* * per-process(per-mm_struct) statistics. */ -#if defined(SPLIT_RSS_COUNTING) -/* - * The mm counters are not protected by its page_table_lock, - * so must be incremented atomically. - */ static inline void set_mm_counter(struct mm_struct *mm, int member, long value) { atomic_long_set(&mm->rss_stat.count[member], value); } +#if defined(SPLIT_RSS_COUNTING) unsigned long get_mm_counter(struct mm_struct *mm, int member); - -static inline void add_mm_counter(struct mm_struct *mm, int member, long value) -{ - atomic_long_add(value, &mm->rss_stat.count[member]); -} - -static inline void inc_mm_counter(struct mm_struct *mm, int member) -{ - atomic_long_inc(&mm->rss_stat.count[member]); -} - -static inline void dec_mm_counter(struct mm_struct *mm, int member) -{ - atomic_long_dec(&mm->rss_stat.count[member]); -} - -#else /* !USE_SPLIT_PTLOCKS */ -/* - * The mm counters are protected by its page_table_lock, - * so can be incremented directly. - */ -static inline void set_mm_counter(struct mm_struct *mm, int member, long value) -{ - mm->rss_stat.count[member] = value; -} - +#else static inline unsigned long get_mm_counter(struct mm_struct *mm, int member) { - return mm->rss_stat.count[member]; + return atomic_long_read(&mm->rss_stat.count[member]); } +#endif static inline void add_mm_counter(struct mm_struct *mm, int member, long value) { - mm->rss_stat.count[member] += value; + atomic_long_add(value, &mm->rss_stat.count[member]); } static inline void inc_mm_counter(struct mm_struct *mm, int member) { - mm->rss_stat.count[member]++; + atomic_long_inc(&mm->rss_stat.count[member]); } static inline void dec_mm_counter(struct mm_struct *mm, int member) { - mm->rss_stat.count[member]--; + atomic_long_dec(&mm->rss_stat.count[member]); } -#endif /* !USE_SPLIT_PTLOCKS */ - static inline unsigned long get_mm_rss(struct mm_struct *mm) { return get_mm_counter(mm, MM_FILEPAGES) + diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index ca01ab2..b8ca318 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -205,19 +205,16 @@ enum { #if USE_SPLIT_PTLOCKS && defined(CONFIG_MMU) #define SPLIT_RSS_COUNTING -struct mm_rss_stat { - atomic_long_t count[NR_MM_COUNTERS]; -}; /* per-thread cached information, */ struct task_rss_stat { int events; /* for synchronization threshold */ int count[NR_MM_COUNTERS]; }; -#else /* !USE_SPLIT_PTLOCKS */ +#endif /* USE_SPLIT_PTLOCKS */ + struct mm_rss_stat { - unsigned long count[NR_MM_COUNTERS]; + atomic_long_t count[NR_MM_COUNTERS]; }; -#endif /* !USE_SPLIT_PTLOCKS */ struct mm_struct { struct vm_area_struct * mmap; /* list of VMAs */ -- 1.7.4.4