[JFFS2] Use yield() between GC passes in background thread.
The garbage collection thread is strictly an optimisation. Everything it does would also be done just-in-time in the context of something in userspace trying to access the file system. Sometimes, however, it's a pessimisation. Especially during early boot when it's checksumming nodes and scanning inodes which are shortly going to be pulled in by read_inode anyway. We end up building the rbtree of node coverage twice for the same inode. By switching to yield() instead of cond_resched() in the main loop, we observe boot times on the OLPC system going down from about 100 seconds to 60. Signed-off-by: David Woodhouse <dwmw2@infradead.org>
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@ -99,7 +99,13 @@ static int jffs2_garbage_collect_thread(void *_c)
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if (try_to_freeze())
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continue;
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cond_resched();
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/* This thread is purely an optimisation. But if it runs when
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other things could be running, it actually makes things a
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lot worse. Use yield() and put it at the back of the runqueue
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every time. Especially during boot, pulling an inode in
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with read_inode() is much preferable to having the GC thread
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get there first. */
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yield();
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/* Put_super will send a SIGKILL and then wait on the sem.
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*/
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