ANDROID: mm: swap: export and whitelist get_shadow_from_swap_cache

The shadow entry in the swapcache contains information about
a page that got swapped out during the reclaim which is then used at the
time of refault to determine if a page is going to be a workingset or
not.

Once the page is swapped out, vendors can implement some algorithms on
the swap area to determine if that page can be further pushed down to
slower devices, Eg: say from costly and faster disk to slower disk. But
if a page that is actively used is pushed to slower disk, the swapin is
going to consume time which can show up in PSI events. The side effect
of increased PSI events is, an example, increased kills by LMKD.

Alternatively, vendors can rely on the information stored in the
swapcache and determine if that particular page in the swap can be
further pushed down to slower devices.

Bug: 350429581
Change-Id: Ibeee10d40cc917229fe3b0fd9a6ef34ad27033e1
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>

mm/swap_state.c

@@ -80,6 +80,7 @@ void *get_shadow_from_swap_cache(swp_entry_t entry)
 		return page;
 	return NULL;
 }
+EXPORT_SYMBOL_GPL(get_shadow_from_swap_cache);
 
 /*
  * add_to_swap_cache resembles filemap_add_folio on swapper_space,