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: <CAJuCfpHJ9PwNOqmFOH373gn6Uqa-orG6zP3rqk-_x=GkpUo2+Q@mail.gmail.com>
Date: Wed, 4 Sep 2024 09:18:01 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: John Hubbard <jhubbard@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	kent.overstreet@...ux.dev, corbet@....net, arnd@...db.de, mcgrof@...nel.org, 
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Subject: Re: [PATCH v2 6/6] alloc_tag: config to store page allocation tag
 refs in page flags

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?