Applying the pagecache monitoring patch

[valdis.kletnieks at vt.edu]

On Sat, 27 May 2017 21:59:54 +0800, Yun-Chih Chen said:

> What I did is:
> 1. Checkout to a commit near 2011/7/18 (the latest commit at the time
> the patch was sent)
> 2. Cherry-picked the three commits from tracing/mm
> 3. Apply the patch
>
> I failed at step 3.
>
> Anyone has any suggestion on this?

Step 0: Ask yourself whether 6 year old code is still relevant.
For starters, look at Mel Gorman's comments: https://lkml.org/lkml/2011/7/29/85

Step 1: Double-check that you applied all 5 patches in the series, in the
correct order.

Step 2: Ask yourself if your knowledge of C is up to actually changing
code rather than just applying patches and praying. Some patch issues are
pretty obvious and can be cut-and-pasted into working, others you'll need
to do some actual programming to fix things.

Step 3:  Look at the .rej  reject files that patch leaves, or the <<< === >>>
conflict markers if git fails to merge a patch cleanly.  Figure out if
there's only 1-2 small rejects or if you have 5,384 conflicts that look
like one side was written in C and the other in Jovial.

Step 4: One by one, manually resolve the conflict(s).  Often, this is due to
other unrelated changes adding or removing or changing a line within the
context area of the rejected section of the patch, and it's obvious how to
hand-apply the change.   Sometimes, it's due to an API change, so you'll have
to understand what got changed, and possibly re-work the patch a bit. You'll
be pretty much on your own here, because there are approximately zero kernel
developers that remember the how or why of an API change from years ago.

Step 5: Test.  Prove the patch (a) works and (b) is actually useful.

Step 6: Rework the patch to apply to a current kernel like 4.11 rather
than a 3.0 kernel from 6 years ago.  This is usually the tough part.

Step 7: Read Documentation/process/submitting-patches.rst and submit the patch
so you don't need to keep re-basing it yourself at each new release.
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