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Date:   Thu, 18 Apr 2019 09:18:34 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Jeff Moyer <jmoyer@redhat.com>, Jan Kara <jack@suse.cz>,
        Pankaj Gupta <pagupta@redhat.com>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
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        yuval shaia <yuval.shaia@oracle.com>
Subject: Re: [PATCH v5 1/6] libnvdimm: nd_region flush callback support
Message-ID: <20190418161833.GA22970@infradead.org>
References: <20190410040826.24371-1-pagupta@redhat.com>
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On Thu, Apr 18, 2019 at 09:05:05AM -0700, Dan Williams wrote:
> > > I'd either add a comment about avoiding retpoline overhead here or just
> > > make ->flush == NULL mean generic_nvdimm_flush(). Just so that people don't
> > > get confused by the code.
> >
> > Isn't this premature optimization?  I really don't like adding things
> > like this without some numbers to show it's worth it.
> 
> I don't think it's premature given this optimization technique is
> already being deployed elsewhere, see:
> 
> https://lwn.net/Articles/774347/

For one this one was backed by numbers, and second after feedback
from Linux we switched to the NULL pointer check instead.