From: Eric Sandeen <sandeen@redhat.com>
Date: Thu, 19 Nov 2009 22:40:23 -0500
Subject: [mm] conditional flush in flush_all_zero_pkmaps
Message-id: <4B05C957.3040700@redhat.com>
Patchwork-id: 21446
O-Subject: [PATCH RHEL5.5] conditional flush in flush_all_zero_pkmaps
Bugzilla: 484683
RH-Acked-by: Rik van Riel <riel@redhat.com>

This is for
https://bugzilla.redhat.com/show_bug.cgi?id=484683
Bug 484683 - BUG on ecryptfs file syestem, while running file system stress test against RHEL5.3snap2

They encountered a softlockup apparently from all the k(un)mapping
ecryptfs does ...

The following patch was found to alleviate the problem, and it
is a portion of an upstream commit.  I don't see a problem
with it, but would very much appreciate review by our
mm/* gurus - bearing in mind that eCryptfs is in tech preview,
this was hit under an insanely high load on eCryptfs, and
this is a core mm/* change ...

Thanks,
-Eric

	From: Nick Piggin <npiggin@suse.de>
	Date: Fri, 1 Aug 2008 01:15:21 +0000 (+0200)
	Subject: x86, pat: avoid highmem cache attribute aliasing
	X-Git-Tag: v2.6.28-rc1~713^2~26
	X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=5843d9a4d0ba89719916c8f07fc9c57b7126be6d

	<ERS: snip>

	I've also just added code for conditional flushing if we haven't got
	any dangling highmem aliases -- this should help performance if we
	change page attributes frequently or systems that aren't using much
	highmem pages (eg. if < 4G RAM). Should be turned into 2 patches, but
	just for RFC...

	Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/mm/highmem.c b/mm/highmem.c
index 547afb4..8b1b83d 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -58,6 +58,7 @@ static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
 static void flush_all_zero_pkmaps(void)
 {
 	int i;
+	int need_flush = 0;
 
 	flush_cache_kmaps();
 
@@ -89,8 +90,10 @@ static void flush_all_zero_pkmaps(void)
 			  &pkmap_page_table[i]);
 
 		set_page_address(page, NULL);
+		need_flush = 1;
 	}
-	flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
+	if (need_flush)
+		flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 }
 
 static inline unsigned long map_new_virtual(struct page *page)