Re: [PATCH] Don't update unchanged merge entries

From: Daniel Barkalow <barkalow@iabervon.org>
Date: Mar 16, 2008, 20:00 UTC
Message-ID: <alpine.LNX.1.00.0803161548250.19665@iabervon.org>
In-Reply-To: <alpine.LFD.1.00.0803161136060.3020@woody.linux-foundation.org>

On Sun, 16 Mar 2008, Linus Torvalds wrote:

Show 13 quoted lines

> In commit 34110cd4e394e3f92c01a4709689b384c34645d8 ("Make 'unpack_trees()' 
> have a separate source and destination index") I introduced a really 
> stupid bug in that it would always add merged entries with the CE_UPDATE 
> flag set. That caused us to always re-write the file, even when it was 
> already up-to-date in the source index.
> 
> Not only is that really stupid from a performance angle, but more 
> importantly it's actively wrong: if we have dirty state in the tree when 
> we merge, overwriting it with the result of the merge will incorrectly 
> overwrite that dirty state.
> 
> This trivially fixes the problem - simply don't set the CE_UPDATE flag 
> when the merge result matches the old state.

While you're at it, you should at least fix the comment. I actually think it would be better to have update start out 0 and be set to CE_UPDATE after verify_uptodate() and verify_absent(), since those checks are what verifies that using CE_UPDATE is okay.

	-Daniel
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