ANDROID: mm/shmem: Add a trace hook to get the shmem folio

Add a trace hook whose callback be used to fill the folio that can be
used for shmem fs. This VH also takes the 'shmem_inode_info' which
can contain the vendor specific data.

The hook is used for drivers who may want to manage the pages of
shmem files on their own and do memory allocation optimizations.

Bug: 273448633
Change-Id: Ia48480bba6dba1ee37a3297b69fd61877dae8dc9
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
(cherry picked from commit 3f5a502bcc6eab646bf1bac4f226960a08bcab06)
Signed-off-by: Georgi Djakov <quic_c_gdjako@quicinc.com>

drivers/android/vendor_hooks.c

@@ -187,3 +187,4 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_logbuf);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_logbuf_pr_cont);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_calc_alloc_flags);
 EXPORT_TRACEPOINT_SYMBOL_GPL(android_vh_regmap_update);
+EXPORT_TRACEPOINT_SYMBOL_GPL(android_rvh_shmem_get_folio);

include/trace/hooks/mm.h

@@ -8,6 +8,14 @@
 #define _TRACE_HOOK_MM_H
 
 #include <trace/hooks/vendor_hooks.h>
+
+struct shmem_inode_info;
+struct folio;
+
+DECLARE_RESTRICTED_HOOK(android_rvh_shmem_get_folio,
+			TP_PROTO(struct shmem_inode_info *info, struct folio **folio),
+			TP_ARGS(info, folio), 2);
+
 /*
 
 DECLARE_RESTRICTED_HOOK(android_rvh_set_skip_swapcache_flags,

mm/shmem.c

@@ -43,6 +43,9 @@
 #include <linux/mm_inline.h>
 #include "swap.h"
 
+#undef CREATE_TRACE_POINTS
+#include <trace/hooks/mm.h>
+
 static struct vfsmount *shm_mnt __ro_after_init;
 
 #ifdef CONFIG_SHMEM
@@ -1764,10 +1767,14 @@ static struct folio *shmem_alloc_folio(gfp_t gfp, int order,
 {
 	struct mempolicy *mpol;
 	pgoff_t ilx;
-	struct folio *folio;
+	struct folio *folio = NULL;
 
 	mpol = shmem_get_pgoff_policy(info, index, order, &ilx);
+	trace_android_rvh_shmem_get_folio(info, &folio);
+	if (folio)
+		goto done;
 	folio = folio_alloc_mpol(gfp, order, mpol, ilx, numa_node_id());
+done:
 	mpol_cond_put(mpol);
 
 	return folio;