Re: [PATCH -mm -v10 1/3] mm, THP, swap: Delay splitting THP during swap out

[Johannes Weiner]

On Thu, May 11, 2017 at 10:22:13AM +0900, Minchan Kim wrote:
> 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. :(

This could be nicer indeed. I just don't like the underscore versions
much, but symmetry with get_swap_page() would be nice.

How about put_swap_page()? :)

That can call the appropriate swapcache_free function then.