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Message-ID: <20130421000522.GA5054@thunk.org> Date: Sat, 20 Apr 2013 20:05:22 -0400 From: Theodore Ts'o <tytso@....edu> To: Mel Gorman <mgorman@...e.de> Cc: Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz> Subject: Re: Excessive stall times on ext4 in 3.9-rc2 As an update to this thread, we brought up this issue at LSF/MM, and there is a thought that we should be able to solve this problem by having lock_buffer() check to see if the buffer is locked due to a write being queued, to have the priority of the write bumped up in the write queues to resolve the priority inversion. I believe Jeff Moyer was going to look into this, if I remember correctly. An alternate solution which I've been playing around adds buffer_head flags so we can indicate that a buffer contains metadata and/or should have I/O submitted with the REQ_PRIO flag set. Adding a buffer_head flag for at least BH_Meta is probably a good thing, since that way the blktrace will be properly annotated. Whether we should keep the BH_Prio flag or rely on lock_buffer() automatically raising the priority is, my feeling is that if lock_buffer() can do the right thing, we should probably do it via lock_buffer(). I have a feeling this might be decidedly non-trivial, though, so perhaps we should just doing via BH flags? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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