On Tue, Sep 27, 2016 at 06:52:06PM +0900, Minchan Kim wrote:

On Tue, Sep 27, 2016 at 12:11:17PM +0300, Kirill A. Shutemov wrote:

quoted

On Tue, Sep 27, 2016 at 09:54:12AM +0100, Mel Gorman wrote:

quoted

On Tue, Sep 27, 2016 at 09:30:55AM +0200, Peter Zijlstra wrote:

quoted

quoted

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.

Ahh. Missed that.

-- 
 Kirill A. Shutemov

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