Re: [PATCH] Migration cache

[Hirokazu Takahashi <taka@valinux.co.jp>]

Hi,

> On Thu, Oct 21, 2004 at 08:09:35PM +0100, Hugh Dickins wrote:
> > On Thu, 21 Oct 2004, Marcelo Tosatti wrote:
> > > On Thu, Oct 21, 2004 at 02:10:44AM +0900, Hirokazu Takahashi wrote:
> > > > 
> > > > I guess it would be better to reserve one swap type for the migration
> > > > cache instead of reserving the bit to reduce the impact of the maximum
> > > > number of swap types.
> > 
> > I thought the same ...
> > 
> > > By reserving one swap type we would also use a bit. Using a swap type is 
> > > the same thing as using a bit in the swap pagetableentry. (the swap type 
> > > has 5 bits reserved for swap devices, 2^5 = 32 swap devices).
> > 
> > ... and don't understand your response.
> > 
> > Reserving a swap type leaves 31 swap devices for normal use, okay;
> > but reserving a bit leaves only 16 swap devices for normal use.
> 
> Oh stupid idiot I am! Of course, we can then remove "pte_is_migration" 
> (and all the related pte handling code). 
> 
> Added to TODO list. 
> 
> If anyone wants to contribute that it would be cool cause I'm 
> quite busy with other stuff right now.

The following code is my simple idea, which might help you.


#define MIGRATION_TYPE	(MAX_SWAPFILES - 1)

static inline int pte_is_migration(pte_t pte)
{
	unsigned long swp_type;
	swp_entry_t arch_entry;

	arch_entry = __pte_to_swp_entry(pte);

	swp_type = __swp_type(arch_entry);

	return swp_type == MIGRATION_TYPE;
}

static inline int PageMigration(page)
{ 
      swp_entry_t entry = { .val = page->private,};
      return (PageSwapCache(page) && swp_type(entry) == MIGRATION_TYPE);
}

Thanks,
Hirokazu Takahashi.
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