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Date: Thu, 24 Mar 2016 12:08:55 -0700 (PDT)
From: Hugh Dickins <hughd@google.com>
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To: "Kirill A. Shutemov" <kirill@shutemov.name>
cc: Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>, Vlastimil Babka <vbabka@suse.cz>,
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        Jerome Marchand <jmarchan@redhat.com>, Yang Shi <yang.shi@linaro.org>,
        Sasha Levin <sasha.levin@oracle.com>, Ning Qu <quning@gmail.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCHv4 00/25] THP-enabled tmpfs/shmem
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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