linux-kernel - Re: [PATCH v2 6/6] alloc_tag: config to store page allocation tag refs in page flags

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Message-ID: <slcih7wenfxtffnamxehvipcwnrq4hgrfu4btssezykr6ow3ww@af5jlsc3t52e>
Date: Wed, 4 Sep 2024 12:21:20 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Matthew Wilcox <willy@...radead.org>, 
	John Hubbard <jhubbard@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>, corbet@....net, 
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Subject: Re: [PATCH v2 6/6] alloc_tag: config to store page allocation tag
 refs in page flags

On Wed, Sep 04, 2024 at 09:18:01AM GMT, Suren Baghdasaryan wrote:
> On Tue, Sep 3, 2024 at 7:19 PM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Tue, Sep 03, 2024 at 06:25:52PM -0700, John Hubbard wrote:
> > > The more I read this story, the clearer it becomes that this should be
> > > entirely done by the build system: set it, or don't set it, automatically.
> > >
> > > And if you can make it not even a kconfig item at all, that's probably even
> > > better.
> > >
> > > And if there is no way to set it automatically, then that probably means
> > > that the feature is still too raw to unleash upon the world.
> >
> > I'd suggest that this implementation is just too whack.
> >
> > What if you use a maple tree for this?  For each allocation range, you
> > can store a pointer to a tag instead of storing an index in each folio.
> 
> I'm not sure I understand your suggestion, Matthew. We allocate a
> folio and need to store a reference to the tag associated with the
> code that allocated that folio. We are not operating with ranges here.
> Are you suggesting to use a maple tree instead of page_ext to store
> this reference?

yeah, I don't think the maple tree idea makes any sense either

we already have a way of going from index -> alloc tag, this is just
about how we store the index