linux-kernel - Re: [PATCH 03/18] mm, hugetlb: unify region structure handling

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Date:	Wed, 31 Jul 2013 11:36:13 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	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 03/18] mm, hugetlb: unify region structure handling

On Tue, Jul 30, 2013 at 10:57:37PM +0530, Aneesh Kumar K.V wrote:
> Joonsoo Kim <iamjoonsoo.kim@....com> writes:
> 
> > Currently, to track a reserved and allocated region, we use two different
> > ways for MAP_SHARED and MAP_PRIVATE. For MAP_SHARED, we use
> > address_mapping's private_list and, for MAP_PRIVATE, we use a resv_map.
> > Now, we are preparing to change a coarse grained lock which protect
> > a region structure to fine grained lock, and this difference hinder it.
> > So, before changing it, unify region structure handling.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> > index a3f868a..a1ae3ada 100644
> > --- a/fs/hugetlbfs/inode.c
> > +++ b/fs/hugetlbfs/inode.c
> > @@ -366,7 +366,12 @@ static void truncate_hugepages(struct inode *inode, loff_t lstart)
> >
> >  static void hugetlbfs_evict_inode(struct inode *inode)
> >  {
> > +	struct resv_map *resv_map;
> > +
> >  	truncate_hugepages(inode, 0);
> > +	resv_map = (struct resv_map *)inode->i_mapping->private_data;
> > +	if (resv_map)
> 
> can resv_map == NULL ?

Hello, Aneesh.

Yes, it can.
root inode which is allocated in hugetlbfs_get_root() doesn't allocate a resv_map.

> 
> 
> > +		kref_put(&resv_map->refs, resv_map_release);
> 
> Also the kref_put is confusing. For shared mapping we don't have ref
> count incremented right ? So may be you can directly call
> resv_map_release or add a comment around explaining this more ?

Yes, I can call resv_map_release() directly, but I think that release
via reference management is better than it.

Thanks.

> 
> 
> >  	clear_inode(inode);
> >  }
> >
> > @@ -468,6 +473,11 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
> >  					umode_t mode, dev_t dev)
> >  {
> >  	struct inode *inode;
> > +	struct resv_map *resv_map;
> > +
> > +	resv_map = resv_map_alloc();
> > +	if (!resv_map)
> > +		return NULL;
> 
> -aneesh
> 
> --
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