On Wed, Nov 25, 2015 at 03:46:35PM -0500, Johannes Weiner wrote:
> On Wed, Nov 25, 2015 at 08:31:02PM +0000, Chris Wilson wrote:
> > On Wed, Nov 25, 2015 at 02:06:10PM -0500, Johannes Weiner wrote:
> > > On Wed, Nov 25, 2015 at 06:36:56PM +0000, Chris Wilson wrote:
> > > > +static bool swap_available(void)
> > > > +{
> > > > + return total_swap_pages || frontswap_enabled;
> > > > +}
> > >
> > > If you use get_nr_swap_pages() instead of total_swap_pages, this will
> > > also stop scanning objects once the swap space is full. We do that in
> > > the VM to stop scanning anonymous pages.
> >
> > Thanks. Would EXPORT_SYMBOL_GPL(nr_swap_pages) (or equivalent) be
> > acceptable?
>
> No opposition from me. Just please add a small comment that this is
> for shrinkers with swappable objects.
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 58877312cf6b..1c7861f4c43c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -48,6 +48,14 @@ static sector_t map_swap_entry(swp_entry_t, struct block_device**);
DEFINE_SPINLOCK(swap_lock);
static unsigned int nr_swapfiles;
atomic_long_t nr_swap_pages;
+/*
+ * Some modules use swappable objects and may try to swap them out under
+ * memory pressure (via the shrinker). Before doing so, they may wish to
+ * check to see if any swap space is available. The shrinker also directly
+ * uses the available swap space to determine whether it can swapout
+ * anon pages in the same manner.
+ */
+EXPORT_SYMBOL_GPL(nr_swap_pages);
Something like that, after a couple more edits?
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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