Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763799AbXESRwn (ORCPT ); Sat, 19 May 2007 13:52:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756595AbXESRwg (ORCPT ); Sat, 19 May 2007 13:52:36 -0400 Received: from holomorphy.com ([66.93.40.71]:60724 "EHLO holomorphy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755761AbXESRwf (ORCPT ); Sat, 19 May 2007 13:52:35 -0400 Date: Sat, 19 May 2007 10:53:20 -0700 From: William Lee Irwin III To: Hugh Dickins Cc: Nick Piggin , Linux Kernel Mailing List , Linux Memory Management List , linux-arch@vger.kernel.org Subject: Re: [rfc] increase struct page size?! Message-ID: <20070519175320.GB19966@holomorphy.com> References: <20070518040854.GA15654@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: The Domain of Holomorphy User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6336 Lines: 214 On Fri, 18 May 2007, Nick Piggin wrote: >> If we add 8 bytes to struct page on 64-bit machines, it becomes 64 bytes, >> which is quite a nice number for cache purposes. >> However we don't have to let those 8 bytes go to waste: we can use them >> to store the virtual address of the page, which kind of makes sense for >> 64-bit, because they can likely to use complicated memory models. On Fri, May 18, 2007 at 04:42:10PM +0100, Hugh Dickins wrote: > Sooner rather than later, don't we need those 8 bytes to expand from > atomic_t to atomic64_t _count and _mapcount? Not that we really need > all 64 bits of both, but I don't know how to work atomically with less. > (Why do I have this sneaking feeling that you're actually wanting > to stick something into the lower bits of page->virtual?) I wonder how close we get to overflow on ->_mapcount and ->_count. (untested/uncompiled). -- wli Index: mm-2.6.21/include/linux/mm.h =================================================================== --- mm-2.6.21.orig/include/linux/mm.h 2007-05-19 10:17:17.682653270 -0700 +++ mm-2.6.21/include/linux/mm.h 2007-05-19 10:38:52.376433663 -0700 @@ -248,6 +248,24 @@ * routine so they can be sure the page doesn't go away from under them. */ +static inline struct page *compound_head(struct page *page) +{ + if (unlikely(PageTail(page))) + return page->first_page; + return page; +} + +static inline int page_count(struct page *page) +{ + return atomic_read(&compound_head(page)->_count); +} + +#ifdef CONFIG_ATOMIC_HIWATER +unsigned long count_hiwater(void); +int put_page_testzero(struct page *); +int get_page_unless_zero(struct page *); +void get_page(struct page *); +#else /* !CONFIG_ATOMIC_HIWATER */ /* * Drop a ref, return true if the refcount fell to zero (the page has no users) */ @@ -267,24 +285,13 @@ return atomic_inc_not_zero(&page->_count); } -static inline struct page *compound_head(struct page *page) -{ - if (unlikely(PageTail(page))) - return page->first_page; - return page; -} - -static inline int page_count(struct page *page) -{ - return atomic_read(&compound_head(page)->_count); -} - static inline void get_page(struct page *page) { page = compound_head(page); VM_BUG_ON(atomic_read(&page->_count) == 0); atomic_inc(&page->_count); } +#endif /* !CONFIG_ATOMIC_HIWATER */ static inline struct page *virt_to_head_page(const void *x) { Index: mm-2.6.21/mm/Makefile =================================================================== --- mm-2.6.21.orig/mm/Makefile 2007-05-18 09:58:43.851524250 -0700 +++ mm-2.6.21/mm/Makefile 2007-05-18 09:58:59.484415118 -0700 @@ -31,4 +31,4 @@ obj-$(CONFIG_MIGRATION) += migrate.o obj-$(CONFIG_SMP) += allocpercpu.o obj-$(CONFIG_QUICKLIST) += quicklist.o - +obj-$(CONFIG_ATOMIC_HIWATER) += atomic-hiwater.o Index: mm-2.6.21/mm/atomic-hiwater.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ mm-2.6.21/mm/atomic-hiwater.c 2007-05-19 10:46:09.713356074 -0700 @@ -0,0 +1,63 @@ +#include +#include +#include +#include +#include +#include + +static DEFINE_PER_CPU(unsigned long, __count_hiwater); + +unsigned long count_hiwater(void) +{ + int cpu; + unsigned long *hiwater, count = 0; + + for_each_online_cpu(cpu) { + hiwater = &per_cpu(__count_hiwater, cpu); + if (*hiwater > count) + count = *hiwater; + } + return count; +} +EXPORT_SYMBOL_GPL(count_hiwater); + +static void update_count_hiwater(unsigned long count) +{ + unsigned long flags, *hiwater; + + local_irq_save(flags); + hiwater = &__get_cpu_var(__count_hiwater); + if (unlikely(count > *hiwater)) + *hiwater = count; + local_irq_restore(flags); +} + +int get_page_unless_zero(struct page *page) +{ + int ret; + + VM_BUG_ON(PageCompound(page)); + ret = atomic_inc_not_zero(&page->_count); + update_count_hiwater(atomic_read(&page->_count)); + return ret; +} +EXPORT_SYMBOL(get_page_unless_zero); + +void get_page(struct page *page) +{ + page = compound_head(page); + VM_BUG_ON(atomic_read(&page->_count) == 0); + update_count_hiwater(atomic_inc_return(&page->_count)); +} +EXPORT_SYMBOL(get_page); + +int put_page_testzero(struct page *page) +{ + int count; + + VM_BUG_ON(atomic_read(&page->_count) == 0); + count = atomic_dec_return(&page->_count); + update_count_hiwater(count); + return count; +} +EXPORT_SYMBOL(put_page_testzero); Index: mm-2.6.21/mm/Kconfig =================================================================== --- mm-2.6.21.orig/mm/Kconfig 2007-05-19 10:20:24.361291479 -0700 +++ mm-2.6.21/mm/Kconfig 2007-05-19 10:22:17.231723598 -0700 @@ -168,3 +168,8 @@ depends on QUICKLIST default "1" +config ATOMIC_HIWATER + bool "Track page reference count high watermarks." + default n + help + This option tracks the largest reference counts seen for a page. Index: mm-2.6.21/mm/vmstat.c =================================================================== --- mm-2.6.21.orig/mm/vmstat.c 2007-05-19 10:34:41.382130313 -0700 +++ mm-2.6.21/mm/vmstat.c 2007-05-19 10:38:38.519644010 -0700 @@ -607,6 +607,29 @@ return v + *pos; } +#ifdef CONFIG_ATOMIC_HIWATER +static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos) +{ + (*pos)++; + if (*pos == ARRAY_SIZE(vmstat_text)) + return (void *)~0UL; + else if (*pos > ARRAY_SIZE(vmstat_text)) + return NULL; + return (unsigned long *)m->private + *pos; +} + +static int vmstat_show(struct seq_file *m, void *arg) +{ + unsigned long *l = arg; + unsigned long off = l - (unsigned long *)m->private; + + if (off < ARRAY_SIZE(vmstat_text)) + seq_printf(m, "%s %lu\n", vmstat_text[off], *l); + else + seq_printf(m, "count_hiwater %lu\n", count_hiwater()); + return 0; +} +#else /* !CONFIG_ATOMIC_HIWATER */ static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos) { (*pos)++; @@ -623,6 +646,7 @@ seq_printf(m, "%s %lu\n", vmstat_text[off], *l); return 0; } +#endif /* !CONFIG_ATOMIC_HIWATER */ static void vmstat_stop(struct seq_file *m, void *arg) { - 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/