From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Zijlstra <peterz@infradead.org>, Nick Piggin <npiggin@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Bob Peterson <rpeterso@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Steven Whitehouse <swhiteho@redhat.com>,
Andrew Lutomirski <luto@kernel.org>,
Andreas Gruenbacher <agruenba@redhat.com>,
Mel Gorman <mgorman@techsingularity.net>,
linux-mm <linux-mm@kvack.org>
Subject: Re: [RFC][PATCH] make global bitlock waitqueues per-node
Date: Wed, 21 Dec 2016 10:02:27 -0800 [thread overview]
Message-ID: <CA+55aFx-YmpZ4NBU0oSw_iJV8jEMaL8qX-HCH=DrutQ65UYR5A@mail.gmail.com> (raw)
In-Reply-To: <20161221083247.GW3174@twins.programming.kicks-ass.net>
On Wed, Dec 21, 2016 at 12:32 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> FWIW, here's mine.. compiles and boots on a NUMA x86_64 machine.
So I like how your patch is smaller, but your patch is also broken.
First off, the whole contention bit is *not* NUMA-specific. It should
help non-NUMA too, by avoiding the stupid extra cache miss.
Secondly, CONFIG_NUMA is a broken thing to test anyway, since adding a
bit for the NUMA case can overflow the page flags as far as I can tell
(MIPS seems to support NUMA on 32-bit, for example, but I didn't
really check the Kconfig details). Making it dependent on 64-bit might
be ok (and would fix the issue above - I don't think we really need to
care too much about 32-bit any more)
But making it conditional at all means that now you have those two
different cases for this, which is a maintenance nightmare. So don't
do it even if we could say "screw 32-bit".
Anyway, the conditional thing could be fixed by just taking Nick's
patch 1/2, and your patch (with the conditional bits stripped out).
I do think your approach of just re-using the existing bit waiting
with just a page-specific waiting function is nicer than Nick's "let's
just roll new waiting functions" approach. It also avoids the extra
initcall.
Nick, comments?
Hugh - mind testing PeterZ's patch too? My comments about the
conditional PG_waiters bit and page bit overflow are not relevant for
your particular scenario, so you can ignore that part, and just take
PaterZ's patch directly.
Linus
next prev parent reply other threads:[~2016-12-21 18:02 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-19 22:58 [RFC][PATCH] make global bitlock waitqueues per-node Dave Hansen
[not found] ` <CA+55aFwK6JdSy9v_BkNYWNdfK82sYA1h3qCSAJQ0T45cOxeXmQ@mail.gmail.com>
2016-12-20 0:20 ` Dave Hansen
2016-12-20 2:31 ` Nicholas Piggin
2016-12-20 12:58 ` Mel Gorman
2016-12-20 13:21 ` Nicholas Piggin
2016-12-20 17:31 ` Linus Torvalds
2016-12-20 18:02 ` Linus Torvalds
2016-12-21 8:09 ` Peter Zijlstra
2016-12-21 8:32 ` Peter Zijlstra
2016-12-21 18:02 ` Linus Torvalds [this message]
2016-12-21 18:33 ` Nicholas Piggin
2016-12-21 19:01 ` Nicholas Piggin
2016-12-21 19:50 ` Linus Torvalds
2016-12-22 2:07 ` Nicholas Piggin
2016-12-22 19:28 ` Hugh Dickins
2016-12-21 10:26 ` Nicholas Piggin
2016-12-20 2:26 ` Nicholas Piggin
2016-12-21 12:30 ` Nicholas Piggin
2016-12-21 18:12 ` Linus Torvalds
2016-12-21 18:40 ` Nicholas Piggin
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