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Make taskq_member() use ->journal_info

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The ->journal_info pointer in the task_struct is reserved for use by
filesystems and because the kernel can have multiple file systems on the
same stack due to direct reclaim, each filesystem that touches
->journal_info in a callback function will save the value at the start
of its frame and restore it at the end of its frame.  This allows us to
safely use ->journal_info to store a pointer to the taskq's struct in
taskq threads so that ZFS code paths can detect the presence of a taskq.
This could break if the ZFS code were to use taskq_member from the
context of direct reclaim. However, there are no such uses of it in that
manner, so this is safe.

This eliminates an O(N) list traversal under a spinlock with an O(1)
unlocked pointer comparison.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: tuxoko <tuxoko@gmail.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes #500
This commit is contained in:
Richard Yao
2015-12-03 14:15:16 -05:00
committed by Brian Behlendorf
parent 1683e75edc
commit a430c11f0b
2 changed files with 4 additions and 35 deletions
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include/sys/taskq.h
+1 -1
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@@ -124,7 +124,7 @@ extern void taskq_wait_id(taskq_t *, taskqid_t);
extern void taskq_wait_outstanding(taskq_t *, taskqid_t);
extern void taskq_wait(taskq_t *);
extern int taskq_cancel_id(taskq_t *, taskqid_t);
extern int taskq_member(taskq_t *, void *);
#define taskq_member(taskq, thread) ((taskq) == ((thread)->journal_info))
#define taskq_create_proc(name, nthreads, pri, min, max, proc, flags) \
taskq_create(name, nthreads, pri, min, max, flags)