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().

This commit is a squash of changes that contains all the fixes in the
reclaim_shmem_address_space() API.

Bug: 201263305
Bug: 263340150
Change-Id: I03d2c3b9610612af977f89ddeabb63b8e9e50918
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
(cherry picked from commit 81102cdb3d594c164676eef4afec4b3c48b55392)
[georgi: Replace page_isolate_lru() with folio_isolate_lru()]
Signed-off-by: Georgi Djakov <quic_c_gdjako@quicinc.com>

include/linux/mm.h

@@ -4072,6 +4072,7 @@ 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);
 
 #ifdef CONFIG_PRINTK
 void mem_dump_obj(void *object);

mm/shmem.c

@@ -40,6 +40,7 @@
 #include <linux/fs_parser.h>
 #include <linux/swapfile.h>
 #include <linux/iversion.h>
+#include <linux/mm_inline.h>
 #include "swap.h"
 
 static struct vfsmount *shm_mnt __ro_after_init;
@@ -5369,3 +5370,41 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 	return page;
 }
 EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
+
+int reclaim_shmem_address_space(struct address_space *mapping)
+{
+#ifdef CONFIG_SHMEM
+	pgoff_t start = 0;
+	struct page *page;
+	LIST_HEAD(page_list);
+	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 (!folio_isolate_lru(page_folio(page)))
+			continue;
+
+		list_add(&page->lru, &page_list);
+
+		if (need_resched()) {
+			xas_pause(&xas);
+			cond_resched_rcu();
+		}
+	}
+	rcu_read_unlock();
+
+	return reclaim_pages(&page_list);
+#else
+	return 0;
+#endif
+}
+EXPORT_SYMBOL_GPL(reclaim_shmem_address_space);