On 11/28/2016 11:00 AM, Christoph Hellwig wrote:
On Mon, Nov 28, 2016 at 10:58:24AM +0200, Avi Kivity wrote:
What I guess is happening is that since the NVMe queue depth is so high, and
request the driver receives is sent immediately to the disk and there is
nothing to merge it to. That could indicate the absence of plugging, or
just a reluctance to merge TRIMs.
That is exactly the case, and it's also an issue with online trim.
I have work in progress block layer trim patches that always plug trims
and have various TRIM merge improvements including support for ranged
TRIMs. It needs a bit more work, but I hope I can post it later
this week.
Great, good to know.
I still think it should also be fixed in the RAID layer. There's no
reason to break a single request in millions of smaller ones, then try
to merge them into one request back again. The queuing layer can merge
when it's given bad patterns from uncontrolled sources, not as an excuse
to generate bad patterns from within the kernel.
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