suse xfs patches

suse xfs patches

[Christoph Hellwig]

Hi Neil, hi Goldwyn,

if you find issue with XFS and commit local patches to the SLES tree
it would be very much appreciated if you could actually send them
upstream, including an explanation of what you are running into.

Thanks a lot,
	Christoph

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Re: suse xfs patches

[Goldwyn Rodrigues]

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On Tue, Jun 14, 2011 at 04:12:38PM -0400, Christoph Hellwig wrote:
> Hi Neil, hi Goldwyn,
> 
> if you find issue with XFS and commit local patches to the SLES tree
> it would be very much appreciated if you could actually send them
> upstream, including an explanation of what you are running into.
> 

Yes sure. I suppose you are refering to the patch attached.
I did not send it upstream because the upstream code had taken a
different approach and the patch was relevant to the SLES kernel
tree only.

FWIW, SGI was involved.

The upstream commits were 90810b9e82a36c3c57c1aeb8b2918b242a130b26 and
ff57ab21995a8636cfc72efeebb09cc6034d756f

-- 
Goldwyn

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From: Goldwyn Rodrigues <rgoldwyn@suse.de>
Subject: XFS - Make xfsbufd less aggressive
References: bnc#649473
Patch-mainline: no

xfsbufd and flush threads are in contention of the xfs_buf_t because
flush thread needs to read a buffer (usually for btree metadata)
which is locked for I/O by xfsbufd for writes. This could block
writes for a long time.

After a run of heavy writes (approx 10 minutes), the vmscan code
shrinks slabs, which instructs xfsbufd to flush the slab cache
as well. xfsbufd receives flush requests. However, this is too 
aggressive for xfsbufd, and causes more contention with flush
threads. To make things worse, the xfsbufd_wakeup returns
zero which does not account to the objects it will free.

This patch makes the flushes less aggressive by returning the count
of objects in the list, and force flushes only when priority > 0.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.de>
Signed-off-by: NeilBrown <neilb@suse.de>

---
 fs/xfs/linux-2.6/xfs_buf.c |   17 +++++++++++++----
 fs/xfs/linux-2.6/xfs_buf.h |    3 +++
 2 files changed, 16 insertions(+), 4 deletions(-)

--- linux-2.6.32-SLE11-SP1.orig/fs/xfs/linux-2.6/xfs_buf.c
+++ linux-2.6.32-SLE11-SP1/fs/xfs/linux-2.6/xfs_buf.c
@@ -411,7 +411,7 @@ _xfs_buf_lookup_pages(
 					__func__, gfp_mask);
 
 			XFS_STATS_INC(xb_page_retries);
-			xfsbufd_wakeup(0, gfp_mask);
+			xfsbufd_wakeup(1, gfp_mask);
 			congestion_wait(BLK_RW_ASYNC, HZ/50);
 			goto retry;
 		}
@@ -1565,6 +1565,7 @@ xfs_alloc_delwrite_queue(
 	INIT_LIST_HEAD(&btp->bt_list);
 	INIT_LIST_HEAD(&btp->bt_delwrite_queue);
 	spin_lock_init(&btp->bt_delwrite_lock);
+	atomic_set(&btp->bt_qcount, 0);
 	btp->bt_flags = 0;
 	btp->bt_task = kthread_run(xfsbufd, btp, "xfsbufd");
 	if (IS_ERR(btp->bt_task)) {
@@ -1627,6 +1628,7 @@ xfs_buf_delwri_queue(
 
 	bp->b_flags |= _XBF_DELWRI_Q;
 	list_add_tail(&bp->b_list, dwq);
+	atomic_inc(&bp->b_target->bt_qcount);
 	bp->b_queuetime = jiffies;
 	spin_unlock(dwlk);
 
@@ -1669,16 +1671,22 @@ xfsbufd_wakeup(
 	gfp_t			mask)
 {
 	xfs_buftarg_t		*btp;
+	int count = 0;
 
 	spin_lock(&xfs_buftarg_lock);
 	list_for_each_entry(btp, &xfs_buftarg_list, bt_list) {
 		if (test_bit(XBT_FORCE_SLEEP, &btp->bt_flags))
 			continue;
-		set_bit(XBT_FORCE_FLUSH, &btp->bt_flags);
-		wake_up_process(btp->bt_task);
+		if (list_empty(&btp->bt_delwrite_queue))
+			continue;
+		count += atomic_read(&btp->bt_qcount);
+		if (priority) {
+			set_bit(XBT_FORCE_FLUSH, &btp->bt_flags);
+			wake_up_process(btp->bt_task);
+		}
 	}
 	spin_unlock(&xfs_buftarg_lock);
-	return 0;
+	return count;
 }
 
 /*
@@ -1715,6 +1723,7 @@ xfs_buf_delwri_split(
 					 _XBF_RUN_QUEUES);
 			bp->b_flags |= XBF_WRITE;
 			list_move_tail(&bp->b_list, list);
+			atomic_dec(&bp->b_target->bt_qcount);
 		} else
 			skipped++;
 	}
--- linux-2.6.32-SLE11-SP1.orig/fs/xfs/linux-2.6/xfs_buf.h
+++ linux-2.6.32-SLE11-SP1/fs/xfs/linux-2.6/xfs_buf.h
@@ -125,6 +125,9 @@ typedef struct xfs_buftarg {
 	struct list_head	bt_delwrite_queue;
 	spinlock_t		bt_delwrite_lock;
 	unsigned long		bt_flags;
+#ifndef __GENKSYMS__
+	atomic_t		bt_qcount;
+#endif
 } xfs_buftarg_t;
 
 /*

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Re: suse xfs patches

[Christoph Hellwig]

On Tue, Jun 14, 2011 at 05:05:50PM -0500, Goldwyn Rodrigues wrote:
> 
> Yes sure. I suppose you are refering to the patch attached.
> I did not send it upstream because the upstream code had taken a
> different approach and the patch was relevant to the SLES kernel
> tree only.

That, and "XFS: force log before waiting for a pinned buffer".

They look similar, but different enough from things that we have
in mainline that make me really curious if you a) were hitting the
same things, and b) came to different conclusions under different
workloads.

Looking over it in more detail the bufd patch should be fully superceed
by current mainline code, altough less so by the commit you quote, but
rather by the LRU-ification of the xfs_buf code.

Similarly the other one you quote isn't really related to what you have
in tree, in fact you are still missing that case in the suse tree - the
addition to xfs_buf_lock that you're adding only in one caller was added
in commit ed3b4d6cdc81e8feefdbfa3c584614be301b6d39, but that was still
missing the trylock case.

Either way the mainline code only handles pinned and stale buffers,
which from my understanding are what matters, but the changelog from
Neil reads like he saw a case where even non-stale buffers might
matter - except that it's not explained very well.

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