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Date:   Wed, 20 Sep 2017 14:51:20 -0400
From:   Jeff King <peff@peff.net>
To:     Michael Haggerty <mhagger@alum.mit.edu>
Cc:     Junio C Hamano <gitster@pobox.com>,
        Stefan Beller <sbeller@google.com>,
        Johannes Schindelin <Johannes.Schindelin@gmx.de>,
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        Brandon Williams <bmwill@google.com>, git@vger.kernel.org
Subject: Re: [PATCH v2 13/21] packed_ref_cache: keep the `packed-refs` file
 mmapped if possible
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On Wed, Sep 20, 2017 at 02:40:58PM -0400, Jeff King wrote:

> > +enum mmap_strategy {
> > +	/*
> > +	 * Don't use mmap() at all for reading `packed-refs`.
> > +	 */
> > +	MMAP_NONE,
> > +
> > +	/*
> > +	 * Can use mmap() for reading `packed-refs`, but the file must
> > +	 * not remain mmapped. This is the usual option on Windows,
> > +	 * where you cannot rename a new version of a file onto a file
> > +	 * that is currently mmapped.
> > +	 */
> > +	MMAP_TEMPORARY,
> 
> I suspect you originally distinguished these cases so that NO_MMAP does
> not read into a fake-mmap buffer, followed by us copying it into another
> buffer. But AFAICT we handle the "NONE" and "TEMPORARY" cases exactly
> the same (by just doing a read_in_full() into our own buffer). Do we
> actually need separate strategies?

In case you are reading these sequentially, I think I talked myself into
the utility of this during the next patch. ;)

-Peff