Re: [PATCH] mm/swapfile: fix swapoff vs. software dirty bits

On Thu, 17 Sep 2015 22:31:52 +0300
Cyrill Gorcunov [off-list ref] wrote:

Thus when CONFIG_MEM_SOFT_DIRTY = n, the unuse_pte will be the same
as it were without the patch, calling pte_same.

Now to the bit itself

#ifdef CONFIG_MEM_SOFT_DIRTY
#define _PAGE_SWP_SOFT_DIRTY_PAGE_PSE
#else
#define _PAGE_SWP_SOFT_DIRTY_PAGE_PSE(_AT(pteval_t, 0))
#endif

it's 0 if CONFIG_MEM_SOFT_DIRTY=n, so any setup of this
bit will simply become nop

Ok, that is what I have been missing with my soft dirty patch for s390.
_PAGE_BIT_SOFT_DIRTY is always defined but the _PAGE_SOFT_DIRTY and
_PAGE_SWP_SOFT_DIRTY are conditional. The primitives are always
defined but turn into nops with CONFIG_MEM_SOFT_DIRTY=n.

#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
static inline pte_t pte_swp_mksoft_dirty(pte_t pte)
{
	return pte_set_flags(pte, _PAGE_SWP_SOFT_DIRTY);
}

static inline int pte_swp_soft_dirty(pte_t pte)
{
	return pte_flags(pte) & _PAGE_SWP_SOFT_DIRTY;
}

static inline pte_t pte_swp_clear_soft_dirty(pte_t pte)
{
	return pte_clear_flags(pte, _PAGE_SWP_SOFT_DIRTY);
}
#endif

So I fear I'm lost where this "set" of the bit comes from
when CONFIG_MEM_SOFT_DIRTY=n.

Martin, could you please elaborate? Seems I'm missing
something obvious.

 
It is me who missed something.. thanks for the explanation.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>