Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 30 Aug 2019 15:53:04 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Michal Hocko <mhocko@kernel.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Vlastimil Babka <vbabka@suse.cz>, hannes@cmpxchg.org,
        rientjes@google.com, akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [v2 PATCH -mm] mm: account deferred split THPs into MemAvailable
Message-ID: <20190830125304.m6aouvq5ohkerfls@box>
References: <aaaf9742-56f7-44b7-c3db-ad078b7b2220@suse.cz>
 <20190827120923.GB7538@dhcp22.suse.cz>
 <20190827121739.bzbxjloq7bhmroeq@box>
 <20190827125911.boya23eowxhqmopa@box>
 <d76ec546-7ae8-23a3-4631-5c531c1b1f40@linux.alibaba.com>
 <20190828075708.GF7386@dhcp22.suse.cz>
 <20190828140329.qpcrfzg2hmkccnoq@box>
 <20190828141253.GM28313@dhcp22.suse.cz>
 <20190828144658.ar4fajfuffn6k2ki@black.fi.intel.com>
 <20190828160224.GP28313@dhcp22.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190828160224.GP28313@dhcp22.suse.cz>
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Aug 28, 2019 at 06:02:24PM +0200, Michal Hocko wrote:
> > > 
> > > Any idea about a bad case?
> > 
> > Not really.
> > 
> > How bad you want it to get? How many processes share the page? Access
> > pattern? Locking situation?
> 
> Let's say how hard a regular user can make this?

It bumped to ~170 ms if each THP was mapped 5 times.

Adding ptl contention (tight loop of MADV_DONTNEED) in 3 processes that
maps the page, the time to split bumped to ~740ms.

Overally, it's reasonable to take ~100ms per GB of huge pages as rule of
thumb.

-- 
 Kirill A. Shutemov