From: Minchan Kim <minchan@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Mel Gorman <mgorman@techsingularity.net>,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>,
Rik van Riel <riel@redhat.com>, linux-mm <linux-mm@kvack.org>
Subject: Re: page_waitqueue() considered harmful
Date: Tue, 27 Sep 2016 18:52:06 +0900 [thread overview]
Message-ID: <20160927095206.GA12598@bbox> (raw)
In-Reply-To: <20160927091117.GA23640@node.shutemov.name>
On Tue, Sep 27, 2016 at 12:11:17PM +0300, Kirill A. Shutemov wrote:
> On Tue, Sep 27, 2016 at 09:54:12AM +0100, Mel Gorman wrote:
> > On Tue, Sep 27, 2016 at 09:30:55AM +0200, Peter Zijlstra wrote:
> > > > Also, if those bitlock ops had a different bit that showed contention,
> > > > we could actually skip *all* of this, and just see that "oh, nobody is
> > > > waiting on this page anyway, so there's no point in looking up those
> > > > wait queues". We don't have that many "__wait_on_bit()" users, maybe
> > > > we could say that the bitlocks do have to haev *two* bits: one for the
> > > > lock bit itself, and one for "there is contention".
> > >
> > > That would be fairly simple to implement, the difficulty would be
> > > actually getting a page-flag to use for this. We're running pretty low
> > > in available bits :/
> >
> > Simple is relative unless I drastically overcomplicated things and it
> > wouldn't be the first time. 64-bit only side-steps the page flag issue
> > as long as we can live with that.
>
> Looks like we don't ever lock slab pages. Unless I miss something.
>
> We can try to use PG_locked + PG_slab to indicate contation.
>
> I tried to boot kernel with CONFIG_SLUB + BUG_ON(PageSlab()) in
> trylock/unlock_page() codepath. Works fine, but more inspection is
> required.
SLUB used bit_spin_lock via slab_lock instead of trylock/unlock.
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next prev parent reply other threads:[~2016-09-27 9:52 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-26 20:58 page_waitqueue() considered harmful Linus Torvalds
2016-09-26 21:23 ` Rik van Riel
2016-09-26 21:30 ` Linus Torvalds
2016-09-26 23:11 ` Kirill A. Shutemov
2016-09-27 1:01 ` Rik van Riel
2016-09-27 7:30 ` Peter Zijlstra
2016-09-27 8:54 ` Mel Gorman
2016-09-27 9:11 ` Kirill A. Shutemov
2016-09-27 9:42 ` Mel Gorman
2016-09-27 9:52 ` Minchan Kim [this message]
2016-09-27 12:11 ` Kirill A. Shutemov
2016-09-29 8:01 ` Peter Zijlstra
2016-09-29 12:55 ` Nicholas Piggin
2016-09-29 13:16 ` Peter Zijlstra
2016-09-29 13:54 ` Nicholas Piggin
2016-09-29 15:05 ` Rik van Riel
2016-09-27 8:03 ` Jan Kara
2016-09-27 8:31 ` Mel Gorman
2016-09-27 14:34 ` Peter Zijlstra
2016-09-27 15:08 ` Nicholas Piggin
2016-09-27 16:31 ` Linus Torvalds
2016-09-27 16:49 ` Peter Zijlstra
2016-09-28 10:45 ` Mel Gorman
2016-09-28 11:11 ` Peter Zijlstra
2016-09-28 16:10 ` Linus Torvalds
2016-09-29 13:08 ` Peter Zijlstra
2016-10-03 10:47 ` Mel Gorman
2016-09-27 14:53 ` Nicholas Piggin
2016-09-27 15:17 ` Nicholas Piggin
2016-09-27 16:52 ` Peter Zijlstra
2016-09-27 17:06 ` Nicholas Piggin
2016-09-28 7:05 ` Peter Zijlstra
2016-09-28 11:05 ` Paul E. McKenney
2016-09-28 11:16 ` Peter Zijlstra
2016-09-28 12:58 ` Paul E. McKenney
2016-09-29 1:31 ` Nicholas Piggin
2016-09-29 2:12 ` Paul E. McKenney
2016-09-29 6:21 ` Peter Zijlstra
2016-09-29 6:42 ` Nicholas Piggin
2016-09-29 7:14 ` Peter Zijlstra
2016-09-29 7:43 ` Peter Zijlstra
2016-09-28 7:40 ` Mel Gorman
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