linux-kernel - Re: [PATCHv4 00/25] THP-enabled tmpfs/shmem

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Date:	Thu, 24 Mar 2016 12:08:55 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
cc:	Hugh Dickins <hughd@...gle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Yang Shi <yang.shi@...aro.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Ning Qu <quning@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCHv4 00/25] THP-enabled tmpfs/shmem

On Thu, 24 Mar 2016, Kirill A. Shutemov wrote:
> On Wed, Mar 23, 2016 at 01:09:05PM -0700, Hugh Dickins wrote:
> > The small files thing formed my first impression.  My second
> > impression was similar, when I tried mmap(NULL, size_of_RAM,
> > PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_SHARED, -1, 0) and
> > cycled around the arena touching all the pages (which of
> > course has to push a little into swap): that soon OOMed.
> > 
> > But there I think you probably just have some minor bug to be fixed:
> > I spent a little while trying to debug it, but then decided I'd
> > better get back to writing to you.  I didn't really understand what
> > I was seeing, but when I hacked some stats into shrink_page_list(),
> > converting !is_page_cache_freeable(page) to page_cache_references(page)
> > to return the difference instead of the bool, a large proportion of
> > huge tmpfs pages seemed to have count 1 too high to be freeable at
> > that point (and one huge tmpfs page had a count of 3477).
> 
> I'll reply to your other points later, but first I wanted to address this
> obvious bug.

Thanks.  That works better, but is not yet right: memory isn't freed
as it should be, so when I exit then try to run a second time, the
mmap() just gets ENOMEM (with /proc/sys/vm/overcommit_memory 0):
MemFree is low.  No rush to fix, I've other stuff to do.

I don't get as far as that on the laptop, since the first run is OOM
killed while swapping; but I can't vouch for the OOM-kill-correctness
of the base tree I'm using, and this laptop has a history of OOMing
rather too easily if all's not right.

Hugh