From: Steven Whitehouse <swhiteho@redhat.com>
Subject: [RHEL 5.1] GFS2: panic in unlink (bz #239737) [1/2]
Date: Tue, 19 Jun 2007 16:05:31 +0100
Bugzilla: 239737
Message-Id: <1182265531.8765.88.camel@quoit>
Changelog: [gfs2] panic in unlink


Hi,

This is the first part of two which fixes bz #239737. This part
simplifies and also fixes a bug relating to the acquisition of multiple
glocks. The first part of this patch is taken from the GFS2 -nmw git
tree. The second part of the patch fixes a problem in the kernel's
sort() library function which can cause it to do more comparisons than
is strictly required resulting in both a slow-down whenever this
function is used and also triggering the BUG_ON() in one of the GFS2
comparison functions which doesn't take kindly to being asked to compare
an item with itself. The second part of the patch is taken from the
upstream kernel and its been upstream since October last year. It is the
only upstream patch affecting the sort() function since that time.

The patches in combination have been tested to ensure that they do fix
the original bug as seen. Also the first part of the patch has been
tested on its own to ensure that it does not result in any performance
regression for the postmark benchmark on GFS2.

Steve.

------------------------------------------------------------------
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Fsteve%2Fgfs2-2.6-nmw.git;a=commitdiff_plain;h=a0cf94cbbb0f60b37be626a4aca3054583adf841

[GFS2] Simplify multiple glock aquisition

There is a bug in the code which acquires multiple glocks where if the
initial out-of-order attempt fails part way though we can land up trying
to acquire the wrong number of glocks. This is part of the fix for red
hat bz #239737. The other part of the bz doesn't apply to upstream
kernels since it was fixed by:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=d3717bdf8f08a0e1039158c8bab2c24d20f492b6

Since the out-of-order code doesn't appear to add anything to the
performance of GFS2, this patch just removed it rather than trying to
fix it. It should be much easier to see whats going on here now. In
addition, we don't allocate any memory unless we are using a lot of
glocks (which is a relatively uncommon case).

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
---

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 384cae6..3f0974e 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1327,10 +1327,6 @@ static int nq_m_sync(unsigned int num_gh, struct gfs2_holder *ghs,
  * @num_gh: the number of structures
  * @ghs: an array of struct gfs2_holder structures
  *
- * Figure out how big an impact this function has.  Either:
- * 1) Replace this code with code that calls gfs2_glock_prefetch()
- * 2) Forget async stuff and just call nq_m_sync()
- * 3) Leave it like it is
  *
  * Returns: 0 on success (all glocks acquired),
  *          errno on failure (no glocks acquired)
@@ -1338,62 +1334,28 @@ static int nq_m_sync(unsigned int num_gh, struct gfs2_holder *ghs,
 
 int gfs2_glock_nq_m(unsigned int num_gh, struct gfs2_holder *ghs)
 {
-	int *e;
-	unsigned int x;
-	int borked = 0, serious = 0;
+	struct gfs2_holder *tmp[4];
+	struct gfs2_holder **pph = tmp;
 	int error = 0;
 
-	if (!num_gh)
+	switch(num_gh) {
+	case 0:
 		return 0;
-
-	if (num_gh == 1) {
+	case 1:
 		ghs->gh_flags &= ~(LM_FLAG_TRY | GL_ASYNC);
 		return gfs2_glock_nq(ghs);
-	}
-
-	e = kcalloc(num_gh, sizeof(struct gfs2_holder *), GFP_KERNEL);
-	if (!e)
-		return -ENOMEM;
-
-	for (x = 0; x < num_gh; x++) {
-		ghs[x].gh_flags |= LM_FLAG_TRY | GL_ASYNC;
-		error = gfs2_glock_nq(&ghs[x]);
-		if (error) {
-			borked = 1;
-			serious = error;
-			num_gh = x;
+	default:
+		if (num_gh <= 4)
 			break;
-		}
+		pph = kmalloc(num_gh * sizeof(struct gfs2_holder *), GFP_NOFS);
+		if (!pph)
+			return -ENOMEM;
 	}
 
-	for (x = 0; x < num_gh; x++) {
-		error = e[x] = glock_wait_internal(&ghs[x]);
-		if (error) {
-			borked = 1;
-			if (error != GLR_TRYFAILED && error != GLR_CANCELED)
-				serious = error;
-		}
-	}
-
-	if (!borked) {
-		kfree(e);
-		return 0;
-	}
-
-	for (x = 0; x < num_gh; x++)
-		if (!e[x])
-			gfs2_glock_dq(&ghs[x]);
-
-	if (serious)
-		error = serious;
-	else {
-		for (x = 0; x < num_gh; x++)
-			gfs2_holder_reinit(ghs[x].gh_state, ghs[x].gh_flags,
-					  &ghs[x]);
-		error = nq_m_sync(num_gh, ghs, (struct gfs2_holder **)e);
-	}
+	error = nq_m_sync(num_gh, ghs, pph);
 
-	kfree(e);
+	if (pph != tmp)
+		kfree(pph);
 
 	return error;
 }

Hi,

This is the second part of the fix for bz #239737. Please see the first
part for a full explanation,

Steve.
-----------------------------------------------------------------
From: keios <keios.cn@gmail.com>
Date: Tue, 3 Oct 2006 08:13:49 +0000 (-0700)
Subject: [PATCH] low performance of lib/sort.c
X-Git-Tag: v2.6.19-rc1~361
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=d3717bdf8f08a0e1039158c8bab2c24d20f492b6

[PATCH] low performance of lib/sort.c

It is a non-standard heap-sort algorithm implementation because the index
of child node is wrong .  The sort function still outputs right result, but
the performance is O( n * ( log(n) + 1 ) ) , about 10% ~ 20% worse than
standard algorithm.

Signed-off-by: keios <keios.cn@gmail.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Acked-by: Zou Nan hai <nanhai.zou@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/lib/sort.c b/lib/sort.c
index 5f3b51f..488788b 100644
--- a/lib/sort.c
+++ b/lib/sort.c
@@ -49,15 +49,15 @@ void sort(void *base, size_t num, size_t size,
 	  void (*swap)(void *, void *, int size))
 {
 	/* pre-scale counters for performance */
-	int i = (num/2) * size, n = num * size, c, r;
+	int i = (num/2 - 1) * size, n = num * size, c, r;
 
 	if (!swap)
 		swap = (size == 4 ? u32_swap : generic_swap);
 
 	/* heapify */
 	for ( ; i >= 0; i -= size) {
-		for (r = i; r * 2 < n; r  = c) {
-			c = r * 2;
+		for (r = i; r * 2 + size < n; r  = c) {
+			c = r * 2 + size;
 			if (c < n - size && cmp(base + c, base + c + size) < 0)
 				c += size;
 			if (cmp(base + r, base + c) >= 0)
@@ -69,8 +69,8 @@ void sort(void *base, size_t num, size_t size,
 	/* sort */
 	for (i = n - size; i >= 0; i -= size) {
 		swap(base, base + i, size);
-		for (r = 0; r * 2 < i; r = c) {
-			c = r * 2;
+		for (r = 0; r * 2 + size < i; r = c) {
+			c = r * 2 + size;
 			if (c < i - size && cmp(base + c, base + c + size) < 0)
 				c += size;
 			if (cmp(base + r, base + c) >= 0)