linux-kernel - Re: Futexes & Folios

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Message-ID: <87cz349f93.ffs@tglx>
Date:   Sat, 13 May 2023 21:56:56 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Matthew Wilcox <willy@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        André Almeida <andrealmeid@...lia.com>
Cc:     linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...dia.com>,
        linux-mm@...ck.org
Subject: Re: Futexes & Folios

On Sat, May 13 2023 at 17:16, Matthew Wilcox wrote:

> Here's a patch which converts the futex code from using pages to using
> folios.  I do have some questions.
>
>  - I assume we really do want to base the key on the page offset of the
>    futex in the file.  That is, it's not good enough to base the key
>    on the folio's index because the folio can be split after setting up
>    the key, and if it is we'd then fail to find the futex later.

Correct.

>  - In hugetlbfs, it doesn't matter whether the pgoff is based on base
>    pages or huge page size -- as long as it's consistent between
>    invocations, everything will work

Yes.

The patch looks sane, but I need to have a look with brain more awake

Thanks,

        tglx