From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: ext4 vs btrfs performance on SSD array
Date: Fri, 5 Sep 2014 09:08:08 -0700
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To: NeilBrown <neilb@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>, Dave Chinner <david@fromorbit.com>, Nikolai Grigoriev <ngrigoriev@gmail.com>, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-raid@vger.kernel.org, linux-mm@kvack.org, Jens Axboe <axboe@kernel.dk>
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On Wed, Sep 03, 2014 at 10:01:58AM +1000, NeilBrown wrote:
> Do we still need maximums at all?

I don't think we do.  At least on any system I work with I have to
increase them to get good performance without any adverse effect on
throttling.

> So can we just remove the limit on max_sectors and the RAID5 stripe cache
> size?  I'm certainly keen to remove the later and just use a mempool if the
> limit isn't needed.
> I have seen reports that a very large raid5 stripe cache size can cause
> a reduction in performance.  I don't know why but I suspect it is a bug that
> should be found and fixed.
> 
> Do we need max_sectors ??

I'll send a patch to remove it and watch for the fireworks..