From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f70.google.com (mail-it0-f70.google.com [209.85.214.70]) by kanga.kvack.org (Postfix) with ESMTP id 09A4D280252 for ; Tue, 27 Sep 2016 05:52:16 -0400 (EDT) Received: by mail-it0-f70.google.com with SMTP id o21so24664798itb.2 for ; Tue, 27 Sep 2016 02:52:16 -0700 (PDT) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTP id t205si2687046iod.210.2016.09.27.02.52.14 for ; Tue, 27 Sep 2016 02:52:15 -0700 (PDT) Date: Tue, 27 Sep 2016 18:52:06 +0900 From: Minchan Kim Subject: Re: page_waitqueue() considered harmful Message-ID: <20160927095206.GA12598@bbox> References: <20160927073055.GM2794@worktop> <20160927085412.GD2838@techsingularity.net> <20160927091117.GA23640@node.shutemov.name> MIME-Version: 1.0 In-Reply-To: <20160927091117.GA23640@node.shutemov.name> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Mel Gorman , Peter Zijlstra , Linus Torvalds , Andrew Morton , "Kirill A. Shutemov" , Johannes Weiner , Jan Kara , Rik van Riel , linux-mm 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org