From: Nicholas Piggin <email@example.com>
To: Linus Torvalds <firstname.lastname@example.org>
Cc: Dave Hansen <email@example.com>,
Bob Peterson <firstname.lastname@example.org>,
Linux Kernel Mailing List <email@example.com>,
Steven Whitehouse <firstname.lastname@example.org>,
Andrew Lutomirski <email@example.com>,
Andreas Gruenbacher <firstname.lastname@example.org>,
Peter Zijlstra <email@example.com>,
Mel Gorman <firstname.lastname@example.org>
Subject: Re: [PATCH 2/2] mm: add PageWaiters indicating tasks are waiting for a page bit
Date: Thu, 29 Dec 2016 15:26:15 +1000 [thread overview]
Message-ID: <email@example.com> (raw)
On Wed, 28 Dec 2016 20:16:56 -0800
Linus Torvalds <firstname.lastname@example.org> wrote:
> On Wed, Dec 28, 2016 at 8:08 PM, Nicholas Piggin <email@example.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).
That's a good point -- they're in the same byte, so all architectures
will be able to avoid the extra barrier regardless of how the
primitives are implemented. Good.
> 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.
Yep. I still don't like the name, but now you've got PG_waiters
commented there at least. I'll have to live with it.
If we get more cases that want to use a similar function, we might make
a more general primitive for architectures that can optimize these multi
bit ops better than x86. Actually even x86 would prefer to do load ;
cmpxchg rather than bitop ; load for the cases where condition code can't
be used to check result.
> > 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
It looks good to me.
next prev parent reply other threads:[~2016-12-29 5:26 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-25 3:00 [PATCH 0/2] PageWaiters again Nicholas Piggin
2016-12-25 3:00 ` [PATCH 1/2] mm: Use owner_priv bit for PageSwapCache, valid when PageSwapBacked Nicholas Piggin
2016-12-25 5:13 ` Hugh Dickins
2016-12-25 3:00 ` [PATCH 2/2] mm: add PageWaiters indicating tasks are waiting for a page bit Nicholas Piggin
2016-12-25 21:51 ` Linus Torvalds
2016-12-26 1:16 ` Nicholas Piggin
2016-12-26 19:07 ` Linus Torvalds
2016-12-27 11:19 ` Nicholas Piggin
2016-12-27 18:58 ` Linus Torvalds
2016-12-27 19:23 ` Linus Torvalds
2016-12-27 19:24 ` Linus Torvalds
2016-12-27 19:40 ` Linus Torvalds
2016-12-27 20:17 ` Linus Torvalds
2016-12-28 3:53 ` Nicholas Piggin
2016-12-28 19:17 ` Linus Torvalds
2016-12-29 4:08 ` Nicholas Piggin
2016-12-29 4:16 ` Linus Torvalds
2016-12-29 5:26 ` Nicholas Piggin [this message]
2017-01-03 10:24 ` Mel Gorman
2017-01-03 12:29 ` Nicholas Piggin
2017-01-03 17:18 ` Mel Gorman
2016-12-29 22:16 ` [PATCH] mm/filemap: fix parameters to test_bit() Olof Johansson
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