linux-kernel - Re: [PATCH mmotm/next] mm: memcontrol: rewrite charge API: fix shmem

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Date:	Mon, 30 Jun 2014 18:06:27 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH mmotm/next] mm: memcontrol: rewrite charge API: fix
 shmem_unuse

On Mon, 30 Jun 2014, Andrew Morton wrote:
> On Mon, 30 Jun 2014 17:10:54 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:
> > On Mon, 30 Jun 2014, Andrew Morton wrote:
> > > On Mon, 30 Jun 2014 15:48:39 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:
> > > > -		return 0;
> > > > +		return -EAGAIN;
> > > 
> > > Maybe it's time to document the shmem_unuse_inode() return values.
> > 
> > Oh dear.  I had hoped they would look after themselves.  This one is a
> > private matter between shmem_unuse_inode and its one caller, just below.
> 
> Well, readers of shmem_unuse_inode() won't know that unless we tell them.

Add comments on the private use of -EAGAIN.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---

 mm/shmem.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- 3.16-rc2-mm1+/mm/shmem.c	2014-06-30 15:05:50.736335600 -0700
+++ linux/mm/shmem.c	2014-06-30 18:00:02.820584009 -0700
@@ -611,7 +611,7 @@ static int shmem_unuse_inode(struct shme
 	radswap = swp_to_radix_entry(swap);
 	index = radix_tree_locate_item(&mapping->page_tree, radswap);
 	if (index == -1)
-		return -EAGAIN;
+		return -EAGAIN;	/* tell shmem_unuse we found nothing */
 
 	/*
 	 * Move _head_ to start search for next from here.
@@ -712,6 +712,7 @@ int shmem_unuse(swp_entry_t swap, struct
 		cond_resched();
 		if (error != -EAGAIN)
 			break;
+		/* found nothing in this: move on to search the next */
 	}
 	mutex_unlock(&shmem_swaplist_mutex);
 
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