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Date: Tue, 12 Jun 2018 05:05:47 -0700
From: Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: Re: [PATCH -mm -V3 03/21] mm, THP, swap: Support PMD swap mapping in
 swap_duplicate()
Message-ID: <20180612120547.njpz73dymeru5mzy@ca-dmjordan1.us.oracle.com>
References: <20180523082625.6897-1-ying.huang@intel.com>
 <20180523082625.6897-4-ying.huang@intel.com>
 <20180611204231.ojhlyrbmda6pouxb@ca-dmjordan1.us.oracle.com>
 <87o9ggpzlk.fsf@yhuang-dev.intel.com>
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To: "Huang, Ying" <ying.huang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Andrea Arcangeli <aarcange@redhat.com>, Michal Hocko <mhocko@suse.com>, Johannes Weiner <hannes@cmpxchg.org>, Shaohua Li <shli@kernel.org>, Hugh Dickins <hughd@google.com>, Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>, Dave Hansen <dave.hansen@linux.intel.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Zi Yan <zi.yan@cs.rutgers.edu>

On Tue, Jun 12, 2018 at 11:15:28AM +0800, Huang, Ying wrote:
> "Huang, Ying" <ying.huang@intel.com> writes:
> >> On Wed, May 23, 2018 at 04:26:07PM +0800, Huang, Ying wrote:
> >>> @@ -3516,11 +3512,39 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
> >>
> >> Two comments about this part of __swap_duplicate as long as you're moving it to
> >> another function:
> >>
> >>    } else if (count || has_cache) {
> >>    
> >>    	if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)          /* #1   */
> >>    		count += usage;
> >>    	else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)     /* #2   */
> >>    		err = -EINVAL;
> >>
> >> #1:  __swap_duplicate_locked might use
> >>
> >>     VM_BUG_ON(usage != SWAP_HAS_CACHE && usage != 1);
> >>
> >> to document the unstated assumption that usage is 1 (otherwise count could
> >> overflow).
> >
> > Sounds good.  Will do this.
> 
> Found usage parameter of __swap_duplicate() could be SWAP_MAP_SHMEM too.
> We can improve the parameter checking.  But that appears not belong to
> this series.

Fair enough, I'll see about adding this along with the other patch I'm sending.

Daniel