Re: [PATCH 3/5] Swap Migration V5: migrate_pages() function

[Dave Hansen <haveblue@us.ibm.com>]

On Tue, 2005-11-01 at 02:06 -0600, Rob Landley wrote:
> On Monday 31 October 2005 21:12, Christoph Lameter wrote:
> > Page migration support in vmscan.c
> 
> This has no #ifdef SWAP:
> 
> > + if (PageSwapCache(page)) {
> > +  swp_entry_t swap = { .val = page_private(page) };
> > +  add_to_swapped_list(swap.val);
> > +  __delete_from_swap_cache(page);
> > +  write_unlock_irq(&mapping->tree_lock);
> > +  swap_free(swap);
> > +  __put_page(page); /* The pagecache ref */
> > +  return 1;
> > + }
> 
> But what you removed did:
> 
> > -#ifdef CONFIG_SWAP
> > -  if (PageSwapCache(page)) {
> > -   swp_entry_t swap = { .val = page_private(page) };
> > -   add_to_swapped_list(swap.val);
> > -   __delete_from_swap_cache(page);
> > -   write_unlock_irq(&mapping->tree_lock);
> > -   swap_free(swap);
> > -   __put_page(page); /* The pagecache ref */
> > -   goto free_it;
> > -  }
> > -#endif /* CONFIG_SWAP */
> 
> What happens if you build without swap?

You don't need an explicit #ifdef.

PageSwapCache() has an #ifdef for its declaration which gets it down to
'0'.  That should get gcc to completely kill the if(){} block, with no
explicit #ifdef.  

-- Dave