linux-kernel - Re: [PATCH 17/18] mm, hugetlb: retry if we fail to allocate a hugepage with use

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Message-ID: <1375834724.2134.49.camel@buesod1.americas.hpqcorp.net>
Date:	Tue, 06 Aug 2013 17:18:44 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	David Gibson <david@...son.dropbear.id.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hillf Danton <dhillf@...il.com>
Subject: Re: [PATCH 17/18] mm, hugetlb: retry if we fail to allocate a
 hugepage with use_reserve

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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