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-rw-r--r--fs/xfs/xfs_aops.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 2705f91bdd0d..9d6a67c7d227 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -136,7 +136,20 @@ done:
memalloc_nofs_restore(nofs_flag);
}
-/* Finish all pending io completions. */
+/*
+ * Finish all pending IO completions that require transactional modifications.
+ *
+ * We try to merge physical and logically contiguous ioends before completion to
+ * minimise the number of transactions we need to perform during IO completion.
+ * Both unwritten extent conversion and COW remapping need to iterate and modify
+ * one physical extent at a time, so we gain nothing by merging physically
+ * discontiguous extents here.
+ *
+ * The ioend chain length that we can be processing here is largely unbound in
+ * length and we may have to perform significant amounts of work on each ioend
+ * to complete it. Hence we have to be careful about holding the CPU for too
+ * long in this loop.
+ */
void
xfs_end_io(
struct work_struct *work)
@@ -157,6 +170,7 @@ xfs_end_io(
list_del_init(&ioend->io_list);
iomap_ioend_try_merge(ioend, &tmp);
xfs_end_ioend(ioend);
+ cond_resched();
}
}