From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-f47.google.com (mail-yh0-f47.google.com [209.85.213.47]) by kanga.kvack.org (Postfix) with ESMTP id 05D686B0035 for ; Mon, 16 Dec 2013 19:30:13 -0500 (EST) Received: by mail-yh0-f47.google.com with SMTP id 29so4343665yhl.20 for ; Mon, 16 Dec 2013 16:30:13 -0800 (PST) Received: from mail-pb0-x22e.google.com (mail-pb0-x22e.google.com [2607:f8b0:400e:c01::22e]) by mx.google.com with ESMTPS id 25si14012922yhc.282.2013.12.16.16.30.12 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 16 Dec 2013 16:30:13 -0800 (PST) Received: by mail-pb0-f46.google.com with SMTP id md12so6187856pbc.19 for ; Mon, 16 Dec 2013 16:30:11 -0800 (PST) Date: Mon, 16 Dec 2013 16:29:48 -0800 (PST) From: Hugh Dickins Subject: Re: mm: ptl is not bloated if it fits in pointer In-Reply-To: <20131216135005.AC5FDE0090@blue.fi.intel.com> Message-ID: References: <20131216100446.GT21999@twins.programming.kicks-ass.net> <20131216135005.AC5FDE0090@blue.fi.intel.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Peter Zijlstra , Hugh Dickins , Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon, 16 Dec 2013, Kirill A. Shutemov wrote: > Peter Zijlstra wrote: > > On Mon, Dec 16, 2013 at 01:04:13AM -0800, Hugh Dickins wrote: > > > It's silly to force the 64-bit CONFIG_GENERIC_LOCKBREAK architectures > > > to kmalloc eight bytes for an indirect page table lock: the lock needs > > > to fit in the space that a pointer to it would occupy, not into an int. > > > > Ah, no. A spinlock is very much assumed to be 32bit, any spinlock that's > > bigger than that is bloated. > > > > For the page-frame case we do indeed not care about the strict 32bit but > > more about not being larger than a pointer, however there are already > > other users. > > > > See for instance include/linux/lockref.h and lib/lockref.c, they very > > much require the spinlock to be 32bit and the below would break that. Whoops, yes indeed, I completely missed that BLOATED_SPINLOCKS is being used for two different purposes, which have two different constraints. > > What about this instead? Smoke-tested. Excellent: I haven't tested it at all, but this patch looks to me exactly how it should be done - thanks. > > From d0243ba6bf462a7c0ae4290e1c0dbdae22eaa2a6 Mon Sep 17 00:00:00 2001 > From: "Kirill A. Shutemov" > Date: Mon, 16 Dec 2013 15:36:31 +0200 > Subject: [PATCH] mm: do not allocate page->ptl dynamically, if spinlock_t fits > to long > > In struct page we have enough space to fit long-size page->ptl > there, but we use dynamically-allocated page->ptl if > size(spinlock_t) > sizeof(int). It hurts 64-bit architectures with > CONFIG_GENERIC_LOCKBREAK, where sizeof(spinlock_t) == 8, but it > easily fits into struct page. > > Signed-off-by: Kirill A. Shutemov Acked-by: Hugh Dickins > --- > include/linux/lockref.h | 2 +- > include/linux/mm.h | 6 +++--- > include/linux/mm_types.h | 3 ++- > kernel/bounds.c | 2 +- > mm/memory.c | 2 +- > 5 files changed, 8 insertions(+), 7 deletions(-) > > diff --git a/include/linux/lockref.h b/include/linux/lockref.h > index c8929c3832db..4bfde0e99ed5 100644 > --- a/include/linux/lockref.h > +++ b/include/linux/lockref.h > @@ -19,7 +19,7 @@ > > #define USE_CMPXCHG_LOCKREF \ > (IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \ > - IS_ENABLED(CONFIG_SMP) && !BLOATED_SPINLOCKS) > + IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4) > > struct lockref { > union { > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 1cedd000cf29..35527173cf50 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1317,7 +1317,7 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a > #endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */ > > #if USE_SPLIT_PTE_PTLOCKS > -#if BLOATED_SPINLOCKS > +#if ALLOC_SPLIT_PTLOCKS > extern bool ptlock_alloc(struct page *page); > extern void ptlock_free(struct page *page); > > @@ -1325,7 +1325,7 @@ static inline spinlock_t *ptlock_ptr(struct page *page) > { > return page->ptl; > } > -#else /* BLOATED_SPINLOCKS */ > +#else /* ALLOC_SPLIT_PTLOCKS */ > static inline bool ptlock_alloc(struct page *page) > { > return true; > @@ -1339,7 +1339,7 @@ static inline spinlock_t *ptlock_ptr(struct page *page) > { > return &page->ptl; > } > -#endif /* BLOATED_SPINLOCKS */ > +#endif /* ALLOC_SPLIT_PTLOCKS */ > > static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd) > { > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index bd299418a934..494b328c2a61 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -26,6 +26,7 @@ struct address_space; > #define USE_SPLIT_PTE_PTLOCKS (NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS) > #define USE_SPLIT_PMD_PTLOCKS (USE_SPLIT_PTE_PTLOCKS && \ > IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK)) > +#define ALLOC_SPLIT_PTLOCKS (SPINLOCK_SIZE > BITS_PER_LONG/8) > > /* > * Each physical page in the system has a struct page associated with > @@ -155,7 +156,7 @@ struct page { > * system if PG_buddy is set. > */ > #if USE_SPLIT_PTE_PTLOCKS > -#if BLOATED_SPINLOCKS > +#if ALLOC_SPLIT_PTLOCKS > spinlock_t *ptl; > #else > spinlock_t ptl; > diff --git a/kernel/bounds.c b/kernel/bounds.c > index 5253204afdca..9fd4246b04b8 100644 > --- a/kernel/bounds.c > +++ b/kernel/bounds.c > @@ -22,6 +22,6 @@ void foo(void) > #ifdef CONFIG_SMP > DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS)); > #endif > - DEFINE(BLOATED_SPINLOCKS, sizeof(spinlock_t) > sizeof(int)); > + DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t)); > /* End of constants */ > } > diff --git a/mm/memory.c b/mm/memory.c > index 5d9025f3b3e1..b6e211b779d0 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4271,7 +4271,7 @@ void copy_user_huge_page(struct page *dst, struct page *src, > } > #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */ > > -#if USE_SPLIT_PTE_PTLOCKS && BLOATED_SPINLOCKS > +#if ALLOC_SPLIT_PTLOCKS > bool ptlock_alloc(struct page *page) > { > spinlock_t *ptl; > -- > Kirill A. Shutemov -- 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