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Date: Thu, 11 May 2017 10:22:13 +0900
From: Minchan Kim <minchan@kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Huang, Ying" <ying.huang@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Andrea Arcangeli <aarcange@redhat.com>,
        Ebru Akagunduz <ebru.akagunduz@gmail.com>,
        Michal Hocko <mhocko@kernel.org>, Tejun Heo <tj@kernel.org>,
        Hugh Dickins <hughd@google.com>, Shaohua Li <shli@kernel.org>,
        Rik van Riel <riel@redhat.com>, cgroups@vger.kernel.org
Subject: Re: [PATCH -mm -v10 1/3] mm, THP, swap: Delay splitting THP during
 swap out
Message-ID: <20170511012213.GA27659@bbox>
References: <20170425125658.28684-1-ying.huang@intel.com>
 <20170425125658.28684-2-ying.huang@intel.com>
 <20170427053141.GA1925@bbox>
 <87mvb21fz1.fsf@yhuang-dev.intel.com>
 <20170428084044.GB19510@bbox>
 <20170501104430.GA16306@cmpxchg.org>
 <20170501235332.GA4411@bbox>
 <20170510135654.GD17121@cmpxchg.org>
 <20170510232556.GA26521@bbox>
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On Thu, May 11, 2017 at 08:25:56AM +0900, Minchan Kim wrote:
> On Wed, May 10, 2017 at 09:56:54AM -0400, Johannes Weiner wrote:
> > Hi Michan,
> > 
> > On Tue, May 02, 2017 at 08:53:32AM +0900, Minchan Kim wrote:
> > > @@ -1144,7 +1144,7 @@ void swap_free(swp_entry_t entry)
> > >  /*
> > >   * Called after dropping swapcache to decrease refcnt to swap entries.
> > >   */
> > > -void swapcache_free(swp_entry_t entry)
> > > +void __swapcache_free(swp_entry_t entry)
> > >  {
> > >  	struct swap_info_struct *p;
> > >  
> > > @@ -1156,7 +1156,7 @@ void swapcache_free(swp_entry_t entry)
> > >  }
> > >  
> > >  #ifdef CONFIG_THP_SWAP
> > > -void swapcache_free_cluster(swp_entry_t entry)
> > > +void __swapcache_free_cluster(swp_entry_t entry)
> > >  {
> > >  	unsigned long offset = swp_offset(entry);
> > >  	unsigned long idx = offset / SWAPFILE_CLUSTER;
> > > @@ -1182,6 +1182,14 @@ void swapcache_free_cluster(swp_entry_t entry)
> > >  }
> > >  #endif /* CONFIG_THP_SWAP */
> > >  
> > > +void swapcache_free(struct page *page, swp_entry_t entry)
> > > +{
> > > +	if (!PageTransHuge(page))
> > > +		__swapcache_free(entry);
> > > +	else
> > > +		__swapcache_free_cluster(entry);
> > > +}
> > 
> > I don't think this is cleaner :/

Let's see a example add_to_swap. Without it, it looks like that.

int add_to_swap(struct page *page)
{
        entry = get_swap_page(page);
        ..
        ..
fail:
        if (PageTransHuge(page))
                swapcache_free_cluster(entry);
        else
                swapcache_free(entry);
}

It doesn't looks good to me because get_swap_page hides
where entry allocation is from cluster or slot but when
we free the entry allocated, we should be aware of the
internal and call right function. :(

Do you think it's better still?