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: <keaqrfkkoswtpbtvr3l5oetd4d3ncbpaxsay7dckn74qdob2u2@lohq26fuccib>
Date: Wed, 4 Sep 2024 12:37:47 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Matthew Wilcox <willy@...radead.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>, 
	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 05:35:49PM GMT, Matthew Wilcox wrote:
> On Wed, Sep 04, 2024 at 09:18:01AM -0700, Suren Baghdasaryan wrote:
> > 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?
> 
> I'm saying that a folio has a physical address.  So you can use a physical
> address as an index into a maple tree to store additional information
> instead of using page_ext or trying to hammer the additional information
> into struct page somewhere.

Ah, thanks, that makes more sense.

But it would add a lot of overhead to the page alloc/free paths...