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authorDavid Chinner <dgc@sgi.com>2008-02-05 12:13:32 +1100
committerLachlan McIlroy <lachlan@redback.melbourne.sgi.com>2008-02-07 18:22:51 +1100
commit249a8c1124653fa90f3a3afff869095a31bc229f (patch)
treee0681990b5b61155a64a9fd3c0cf73d4d6bb4ce5 /fs/xfs/xfs_trans.h
parent4576758db5817a91b8974c696247d459dc653db2 (diff)
downloadop-kernel-dev-249a8c1124653fa90f3a3afff869095a31bc229f.zip
op-kernel-dev-249a8c1124653fa90f3a3afff869095a31bc229f.tar.gz
[XFS] Move AIL pushing into it's own thread
When many hundreds to thousands of threads all try to do simultaneous transactions and the log is in a tail-pushing situation (i.e. full), we can get multiple threads walking the AIL list and contending on the AIL lock. The AIL push is, in effect, a simple I/O dispatch algorithm complicated by the ordering constraints placed on it by the transaction subsystem. It really does not need multiple threads to push on it - even when only a single CPU is pushing the AIL, it can push the I/O out far faster that pretty much any disk subsystem can handle. So, to avoid contention problems stemming from multiple list walkers, move the list walk off into another thread and simply provide a "target" to push to. When a thread requires a push, it sets the target and wakes the push thread, then goes to sleep waiting for the required amount of space to become available in the log. This mechanism should also be a lot fairer under heavy load as the waiters will queue in arrival order, rather than queuing in "who completed a push first" order. Also, by moving the pushing to a separate thread we can do more effectively overload detection and prevention as we can keep context from loop iteration to loop iteration. That is, we can push only part of the list each loop and not have to loop back to the start of the list every time we run. This should also help by reducing the number of items we try to lock and/or push items that we cannot move. Note that this patch is not intended to solve the inefficiencies in the AIL structure and the associated issues with extremely large list contents. That needs to be addresses separately; parallel access would cause problems to any new structure as well, so I'm only aiming to isolate the structure from unbounded parallelism here. SGI-PV: 972759 SGI-Modid: xfs-linux-melb:xfs-kern:30371a Signed-off-by: David Chinner <dgc@sgi.com> Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Diffstat (limited to 'fs/xfs/xfs_trans.h')
-rw-r--r--fs/xfs/xfs_trans.h5
1 files changed, 3 insertions, 2 deletions
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index bea6e2b..7f40628 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -992,8 +992,9 @@ int _xfs_trans_commit(xfs_trans_t *,
int *);
#define xfs_trans_commit(tp, flags) _xfs_trans_commit(tp, flags, NULL)
void xfs_trans_cancel(xfs_trans_t *, int);
-void xfs_trans_ail_init(struct xfs_mount *);
-xfs_lsn_t xfs_trans_push_ail(struct xfs_mount *, xfs_lsn_t);
+int xfs_trans_ail_init(struct xfs_mount *);
+void xfs_trans_ail_destroy(struct xfs_mount *);
+void xfs_trans_push_ail(struct xfs_mount *, xfs_lsn_t);
xfs_lsn_t xfs_trans_tail_ail(struct xfs_mount *);
void xfs_trans_unlocked_item(struct xfs_mount *,
xfs_log_item_t *);
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