linux-kernel - Re: [PATCH v2 09/20] mm, hugetlb: protect region tracking via newly introduced resv

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Date:	Tue, 13 Aug 2013 16:45:44 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	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>,
	David Gibson <david@...son.dropbear.id.au>, 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 v2 09/20] mm, hugetlb: protect region tracking via newly
 introduced resv_map lock

> > @@ -202,15 +199,27 @@ static long region_chg(struct resv_map *resv, long f, long t)
> >  	 * Subtle, allocate a new region at the position but make it zero
> >  	 * size such that we can guarantee to record the reservation. */
> >  	if (&rg->link == head || t < rg->from) {
> > -		nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
> > -		if (!nrg)
> > -			return -ENOMEM;
> > +		if (!nrg) {
> > +			nrg = kmalloc(sizeof(*nrg), GFP_NOWAIT);
> > +			if (!nrg) {
> > +				spin_unlock(&resv->lock);
> > +				nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
> > +				if (!nrg) {
> > +					chg = -ENOMEM;
> > +					goto out;
> 
> Just return -ENOMEM here.

Okay. It looks better!

> 
> > +				}
> > +				goto retry;
> > +			}
> > +		}
> > +
> 
> You seem to be right, at least in my workloads, the hold times for the
> region lock is quite small, so a spinlock is better than a sleeping
> lock.
> 
> That said, this code is quite messy, but I cannot think of a
> better/cleaner approach right now.

Okay.

Thanks for review!
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