Message-ID: <1375834724.2134.49.camel@buesod1.americas.hpqcorp.net>
Subject: Re: [PATCH 17/18] mm, hugetlb: retry if we fail to allocate a
 hugepage with use_reserve
From: Davidlohr Bueso <davidlohr@hp.com>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Gibson <david@gibson.dropbear.id.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>,
        Michal Hocko <mhocko@suse.cz>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Hugh Dickins <hughd@google.com>,
        Davidlohr Bueso <davidlohr.bueso@hp.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Wanpeng Li <liwanp@linux.vnet.ibm.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Hillf Danton <dhillf@gmail.com>
Date: Tue, 06 Aug 2013 17:18:44 -0700
In-Reply-To: <20130805073647.GD27240@lge.com>
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	 <20130803104302.GC19115@voom.redhat.com> <20130805073647.GD27240@lge.com>
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On Mon, 2013-08-05 at 16:36 +0900, Joonsoo Kim wrote:
> > Any mapping that doesn't use the reserved pool, not just
> > MAP_NORESERVE.  For example, if a process makes a MAP_PRIVATE mapping,
> > then fork()s then the mapping is instantiated in the child, that will
> > not draw from the reserved pool.
> > 
> > > Should we ensure them to allocate the last hugepage?
> > > They map a region with MAP_NORESERVE, so don't assume that their requests
> > > always succeed.
> > 
> > If the pages are available, people get cranky if it fails for no
> > apparent reason, MAP_NORESERVE or not.  They get especially cranky if
> > it sometimes fails and sometimes doesn't due to a race condition.
> 
> Hello,
> 
> Hmm... Okay. I will try to implement another way to protect race condition.
> Maybe it is the best to use a table mutex :)
> Anyway, please give me a time, guys.

So another option is to take the mutex table patchset for now as it
*does* improve things a great deal, then, when ready, get rid of the
instantiation lock all together.

Thanks,
Davidlohr

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