Re: [PATCH] MD: make bio mergeable

[Shaohua Li]

On Thu, Apr 28, 2016 at 08:00:22PM +0000, Holger Kiehl wrote:
> Hello,
> 
> On Mon, 25 Apr 2016, Shaohua Li wrote:
> 
> > blk_queue_split marks bio unmergeable, which makes sense for normal bio.
> > But if dispatching the bio to underlayer disk, the blk_queue_split
> > checks are invalid, hence it's possible the bio becomes mergeable.
> > 
> > In the reported bug, this bug causes trim against raid0 performance slash
> > https://bugzilla.kernel.org/show_bug.cgi?id=117051
> > 
> This patch makes a huge difference. On a system with two Samsung 850 Pro
> in a MD Raid0 setup the time for fstrim went down from ~30min to 18sec!
> 
> However, on another system with two Intel P3700 1.6TB NVMe PCIe SSD's
> also setup as one big MD Raid0, the patch does not make any difference
> at all. fstrim takes more then 4 hours!

Does the raid0 cross two partitions or two SSD?

can you post blktrace data in the bugzilloa, I'll track the bug there.

Thanks,
Shaohua