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: <CAJuCfpEtsWM2S0K=UB1QZ81qeq_5jY-R0zNz3Kc8WojvJfj76w@mail.gmail.com>
Date: Wed, 4 Sep 2024 09:39:33 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Matthew Wilcox <willy@...radead.org>, John Hubbard <jhubbard@...dia.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, corbet@....net, arnd@...db.de, 
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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 4, 2024 at 9:37 AM Kent Overstreet
<kent.overstreet@...ux.dev> wrote:
>
> 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...

Yeah, inserting into a maple_tree in the fast path of page allocation
would introduce considerable performance overhead.