ANDROID: mm: add reclaim_shmem_address_space() for faster reclaims

Add the functionality that allow users of shmem to reclaim its pages
without going through the kswapd/direct reclaim path. An example usecase
is: Say that device allocates a larger amount of shmem pages and shares
it with hardware. To faster reclaims such pages, drivers can register
the shrinkers and call reclaim_shmem_address_space().

The implementation of this function is mostly borrowed from
reclaim_address_space() implemented for per process reclaim[1].

[1] https://lore.kernel.org/patchwork/cover/378056/

Bug: 201263305
Change-Id: I03d2c3b9610612af977f89ddeabb63b8e9e50918
Signed-off-by: Charan Teja Reddy <quic_charante@quicinc.com>

include/linux/mm.h

@@ -3295,6 +3295,8 @@ unsigned long wp_shared_mapping_range(struct address_space *mapping,
 #endif
 
 extern int sysctl_nr_trim_pages;
+extern int reclaim_shmem_address_space(struct address_space *mapping);
+extern int reclaim_pages_from_list(struct list_head *page_list);
 
 #ifdef CONFIG_PRINTK
 void mem_dump_obj(void *object);

mm/shmem.c

@@ -39,6 +39,7 @@
 #include <linux/frontswap.h>
 #include <linux/fs_parser.h>
 #include <linux/swapfile.h>
+#include <linux/mm_inline.h>
 
 static struct vfsmount *shm_mnt;
 
@@ -4207,3 +4208,41 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 #endif
 }
 EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
+
+int reclaim_shmem_address_space(struct address_space *mapping)
+{
+	pgoff_t start = 0;
+	struct page *page;
+	LIST_HEAD(page_list);
+	int reclaimed;
+	XA_STATE(xas, &mapping->i_pages, start);
+
+	if (!shmem_mapping(mapping))
+		return -EINVAL;
+
+	lru_add_drain();
+
+	rcu_read_lock();
+	xas_for_each(&xas, page, ULONG_MAX) {
+		if (xas_retry(&xas, page))
+			continue;
+		if (xa_is_value(page))
+			continue;
+		if (isolate_lru_page(page))
+			continue;
+
+		list_add(&page->lru, &page_list);
+		inc_node_page_state(page, NR_ISOLATED_ANON +
+				page_is_file_lru(page));
+
+		if (need_resched()) {
+			xas_pause(&xas);
+			cond_resched_rcu();
+		}
+	}
+	rcu_read_unlock();
+	reclaimed = reclaim_pages_from_list(&page_list);
+
+	return reclaimed;
+}
+EXPORT_SYMBOL_GPL(reclaim_shmem_address_space);

mm/vmscan.c

@@ -1868,6 +1868,36 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
 	return nr_reclaimed;
 }
 
+int reclaim_pages_from_list(struct list_head *page_list)
+{
+	struct scan_control sc = {
+		.gfp_mask = GFP_KERNEL,
+		.priority = DEF_PRIORITY,
+		.may_writepage = 1,
+		.may_unmap = 1,
+		.may_swap = 1,
+	};
+	unsigned long nr_reclaimed;
+	struct reclaim_stat dummy_stat;
+	struct page *page;
+
+	list_for_each_entry(page, page_list, lru)
+		ClearPageActive(page);
+
+	nr_reclaimed = shrink_page_list(page_list, NULL, &sc,
+				&dummy_stat, false);
+	while (!list_empty(page_list)) {
+
+		page = lru_to_page(page_list);
+		list_del(&page->lru);
+		dec_node_page_state(page, NR_ISOLATED_ANON +
+				page_is_file_lru(page));
+		putback_lru_page(page);
+	}
+
+	return nr_reclaimed;
+}
+
 /*
  * Attempt to remove the specified page from its LRU.  Only take this page
  * if it is of the appropriate PageActive status.  Pages which are being