linux-kernel - Re: mm: pages are not freed from lru_add

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Message-ID: <20160503100748.GA31787@node.shutemov.name>
Date:	Tue, 3 May 2016 13:07:48 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Shutemov, Kirill" <kirill.shutemov@...el.com>,
	"Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>
Subject: Re: mm: pages are not freed from lru_add_pvecs after process
 termination

On Tue, May 03, 2016 at 09:37:57AM +0200, Michal Hocko wrote:
> On Mon 02-05-16 19:02:50, Kirill A. Shutemov wrote:
> > On Mon, May 02, 2016 at 08:49:03AM -0700, Dave Hansen wrote:
> > > On 05/02/2016 08:01 AM, Kirill A. Shutemov wrote:
> > > > On Mon, May 02, 2016 at 04:39:35PM +0200, Vlastimil Babka wrote:
> > > >> On 04/27/2016 07:11 PM, Dave Hansen wrote:
> > > >>> 6. Perhaps don't use the LRU pagevecs for large pages.  It limits the
> > > >>>    severity of the problem.
> > > >>
> > > >> I think that makes sense. Being large already amortizes the cost per base
> > > >> page much more than pagevecs do (512 vs ~22 pages?).
> > > > 
> > > > We try to do this already, don't we? Any spefic case where we have THPs on
> > > > pagevecs?
> > > 
> > > Lukas was hitting this on a RHEL 7 era kernel.  In his kernel at least,
> > > I'm pretty sure THP's were ending up on pagevecs.  Are you saying you
> > > don't think we're doing that any more?
> > 
> > As Vlastimil pointed, we do. It need to be fixed, I think.
> 
> It seems that offloading the draining to the vmstat context doesn't look
> terribly bad. Don't we rather want to go that way?

Maybe. My knowledge about lru cache is limited.

-- 
 Kirill A. Shutemov