linux-kernel - Re: [PATCH 2/2] mm: add PageWaiters indicating tasks are waiting for a page bit

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Message-ID: <CA+55aFxGz8R8J9jLvKpLUgyhWVYcgtObhbHBP7eZzZyc05AODw@mail.gmail.com>
Date:   Wed, 28 Dec 2016 20:16:56 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Bob Peterson <rpeterso@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-mm <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH 2/2] mm: add PageWaiters indicating tasks are waiting for
 a page bit

On Wed, Dec 28, 2016 at 8:08 PM, Nicholas Piggin <npiggin@...il.com> wrote:
>
> Okay. The name could be a bit better though I think, for readability.
> Just a BUILD_BUG_ON if it is not constant and correct bit numbers?

I have a slightly edited patch - moved the comments around and added
some new comments (about both the sign bit, but also about how the
smp_mb() shouldn't be necessary even for the non-atomic fallback).

I also did a BUILD_BUG_ON(), except the other way around - keeping it
about the sign bit in the byte, just just verifying that yes,
PG_waiters is that sign bit.

> BTW. I just notice in your patch too that you didn't use "nr" in the
> generic version.

And I fixed that too.

Of course, I didn't test the changes (apart from building it). But
I've been running the previous version since yesterday, so far no
issues.

                Linus

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