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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Matthew Wilcox <willy@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Darren Hart <dvhart@infradead.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        =?utf-8?Q?Andr=C3=A9?= Almeida <andrealmeid@igalia.com>
Cc:     linux-kernel@vger.kernel.org, Jason Gunthorpe <jgg@nvidia.com>,
        linux-mm@kvack.org
Subject: Re: Futexes & Folios
In-Reply-To: <ZF+3xpmouwur4sVE@casper.infradead.org>
References: <ZF+3xpmouwur4sVE@casper.infradead.org>
Date:   Sat, 13 May 2023 21:56:56 +0200
Message-ID: <87cz349f93.ffs@tglx>
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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