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From: Hugh Dickins <hugh@veritas.com>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Arjan van de Ven <arjanv@redhat.com>, <linux-kernel@vger.kernel.org>
Subject: [PATCH] revert to static = {0} + comment
Date: Tue, 5 Aug 2003 19:41:19 +0100 (BST)	[thread overview]
Message-ID: <Pine.LNX.4.44.0308051931380.1827-100000@localhost.localdomain> (raw)
In-Reply-To: <1060099637.5308.7.camel@laptop.fenrus.com>

Please revert to static zero initialization of a const: when thus
initialized it's linked into a readonly cacheline shared between cpus;
otherwise it's linked into bss, likely to be in a dirty cacheline
bouncing between cpus.

On 5 Aug 2003, Arjan van de Ven wrote:
> how about adding a big fat comment here that says this?
> Otherwise this keeps happening all the time...
and others concurred.

Okay, by popular request, here it is with a small thin comment.

--- 2.6.0-test2-bk/mm/shmem.c	Tue Aug  5 15:57:31 2003
+++ linux/mm/shmem.c	Tue Aug  5 19:29:16 2003
@@ -296,7 +296,8 @@
 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 	struct page *page = NULL;
 	swp_entry_t *entry;
-	static const swp_entry_t unswapped;
+	static const swp_entry_t unswapped = {0};
+	/* = {0} to go in readonly data, to avoid bss cacheline bounce */
 
 	if (sgp != SGP_WRITE &&
 	    ((loff_t) index << PAGE_CACHE_SHIFT) >= i_size_read(inode))


  reply	other threads:[~2003-08-05 18:39 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-08-05 15:48 [PATCH] revert to static = {0} Hugh Dickins
2003-08-05 16:07 ` Arjan van de Ven
2003-08-05 18:41   ` Hugh Dickins [this message]
2003-08-05 16:09 ` Randy.Dunlap
2003-08-05 18:49   ` Hugh Dickins
2003-08-05 16:18 ` Lou Langholtz
2003-08-05 17:44 ` Jeff Garzik
2003-08-05 18:51   ` Hugh Dickins
2003-08-05 19:06     ` William Lee Irwin III
2003-08-05 21:13       ` Jeff Garzik

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