linux-kernel - Re: [PATCH 1/5] mm: memcontrol: generalize locking for the page->mem

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Message-ID: <20160129164353.GA8845@cmpxchg.org>
Date:	Fri, 29 Jan 2016 11:43:53 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...com
Subject: Re: [PATCH 1/5] mm: memcontrol: generalize locking for the
 page->mem_cgroup binding

On Wed, Jan 27, 2016 at 05:30:45PM +0300, Vladimir Davydov wrote:
> On Tue, Jan 26, 2016 at 04:00:02PM -0500, Johannes Weiner wrote:
> 
> > @@ -683,17 +683,17 @@ int __set_page_dirty_buffers(struct page *page)
> >  		} while (bh != head);
> >  	}
> >  	/*
> > -	 * Use mem_group_begin_page_stat() to keep PageDirty synchronized with
> > -	 * per-memcg dirty page counters.
> > +	 * Lock out page->mem_cgroup migration to keep PageDirty
> > +	 * synchronized with per-memcg dirty page counters.
> >  	 */
> > -	memcg = mem_cgroup_begin_page_stat(page);
> > +	memcg = lock_page_memcg(page);
> >  	newly_dirty = !TestSetPageDirty(page);
> >  	spin_unlock(&mapping->private_lock);
> >  
> >  	if (newly_dirty)
> >  		__set_page_dirty(page, mapping, memcg, 1);
> 
> Do we really want to pass memcg to __set_page_dirty and then to
> account_page_dirtied, increasing stack/regs usage even in case memory
> cgroup is disabled? May be, it'd be better to make
> mem_cgroup_update_page_stat take a page instead of a memcg?

I'll look into that. It will need changing migration to leave the
page->mem_cgroup binding of live pages alone, but that's something
worth doing anyway. It's beyond the scope of these patches, though.

Thanks