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SubjectRe: [PATCH 0/4] btrfs: Convert kmaps to core page calls
On Tue, Feb 09, 2021 at 04:11:23PM +0100, David Sterba wrote:
> On Fri, Feb 05, 2021 at 03:23:00PM -0800, wrote:
> > From: Ira Weiny <>
> >
> > There are many places where kmap/<operation>/kunmap patterns occur. We lift
> > these various patterns to core common functions and use them in the btrfs file
> > system. At the same time we convert those core functions to use
> > kmap_local_page() which is more efficient in those calls.
> >
> > I think this is best accepted through Andrew's tree as it has the mem*_page
> > functions in it. But I'd like to get an ack from David or one of the other
> > btrfs maintainers before the btrfs patches go through.
> I'd rather take the non-mm patches through my tree so it gets tested
> the same way as other btrfs changes, straightforward cleanups or not.


> This brings the question how to do that as the first patch should go
> through the MM tree. One option is to posptpone the actual cleanups
> after the 1st patch is merged but this could take a long delay.
> I'd suggest to take the 1st patch within MM tree in the upcoming merge
> window and then I can prepare a separate pull with just the cleanups.
> Removing an inter-tree patch dependency was a sufficient reason for
> Linus in the past for such pull requests.

There are others how want this base patch too.[1] So I like this option.

> > There are a lot more kmap->kmap_local_page() conversions but kmap_local_page()
> > requires some care with the unmapping order and so I'm still reviewing those
> > changes because btrfs uses a lot of loops for it's kmaps.
> It sounds to me that converting the kmaps will take some time anyway so
> exporting the helpers first and then converting the subsystems might be
> a good option. In case you'd like to get rid of the simple cases in
> btrfs code now we can do the 2 pull requests.

I would really like to get the simple case out of the way because the next
series has more difficult changes and the simple cases always cause me trouble
when grepping/coccinelle'ing for things.

So I would like a follow on pull request if possible. But I'm willing to do
what works best for you.

For now I will spin a new version with the changes you've requested ASAP.



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