[PATCH v9 11/19] zram: move post-processing target allocation

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Allocate post-processing target in place_pp_slot().  This
simplifies scan_slots_for_writeback() and scan_slots_for_recompress()
loops because we don't need to track pps pointer state anymore.
Previously we have to explicitly NULL the point if it has been added
to a post-processing bucket or re-use previously allocated pointer
otherwise and make sure we don't leak the memory in the end.

We are also fine doing GFP_NOIO allocation, as post-processing can
be called under memory pressure so we better pick as many slots as
we can as soon as we can and start post-processing them, possibly
saving the memory.  Allocation failure there is not fatal, we will
post-process whatever we put into the buckets on previous
iterations.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 50 +++++++++++++++--------------------
 1 file changed, 22 insertions(+), 28 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 6755ca90f737..7ad89df9a304 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -295,15 +295,24 @@ static void release_pp_ctl(struct zram *zram, struct zram_pp_ctl *ctl)
 	kfree(ctl);
 }
 
-static void place_pp_slot(struct zram *zram, struct zram_pp_ctl *ctl,
-			  struct zram_pp_slot *pps)
+static bool place_pp_slot(struct zram *zram, struct zram_pp_ctl *ctl,
+			  u32 index)
 {
-	u32 idx;
+	struct zram_pp_slot *pps;
+	u32 bid;
+
+	pps = kmalloc(sizeof(*pps), GFP_NOIO | __GFP_NOWARN);
+	if (!pps)
+		return false;
 
-	idx = zram_get_obj_size(zram, pps->index) / PP_BUCKET_SIZE_RANGE;
-	list_add(&pps->entry, &ctl->pp_buckets[idx]);
+	INIT_LIST_HEAD(&pps->entry);
+	pps->index = index;
+
+	bid = zram_get_obj_size(zram, pps->index) / PP_BUCKET_SIZE_RANGE;
+	list_add(&pps->entry, &ctl->pp_buckets[bid]);
 
 	zram_set_flag(zram, pps->index, ZRAM_PP_SLOT);
+	return true;
 }
 
 static struct zram_pp_slot *select_pp_slot(struct zram_pp_ctl *ctl)
@@ -737,15 +746,8 @@ static int scan_slots_for_writeback(struct zram *zram, u32 mode,
 				    unsigned long index,
 				    struct zram_pp_ctl *ctl)
 {
-	struct zram_pp_slot *pps = NULL;
-
 	for (; nr_pages != 0; index++, nr_pages--) {
-		if (!pps)
-			pps = kmalloc(sizeof(*pps), GFP_KERNEL);
-		if (!pps)
-			return -ENOMEM;
-
-		INIT_LIST_HEAD(&pps->entry);
+		bool ok = true;
 
 		zram_slot_lock(zram, index);
 		if (!zram_allocated(zram, index))
@@ -765,14 +767,13 @@ static int scan_slots_for_writeback(struct zram *zram, u32 mode,
 		    !zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
 			goto next;
 
-		pps->index = index;
-		place_pp_slot(zram, ctl, pps);
-		pps = NULL;
+		ok = place_pp_slot(zram, ctl, index);
 next:
 		zram_slot_unlock(zram, index);
+		if (!ok)
+			break;
 	}
 
-	kfree(pps);
 	return 0;
 }
 
@@ -1827,16 +1828,10 @@ static int scan_slots_for_recompress(struct zram *zram, u32 mode, u32 prio_max,
 				     struct zram_pp_ctl *ctl)
 {
 	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
-	struct zram_pp_slot *pps = NULL;
 	unsigned long index;
 
 	for (index = 0; index < nr_pages; index++) {
-		if (!pps)
-			pps = kmalloc(sizeof(*pps), GFP_KERNEL);
-		if (!pps)
-			return -ENOMEM;
-
-		INIT_LIST_HEAD(&pps->entry);
+		bool ok = true;
 
 		zram_slot_lock(zram, index);
 		if (!zram_allocated(zram, index))
@@ -1859,14 +1854,13 @@ static int scan_slots_for_recompress(struct zram *zram, u32 mode, u32 prio_max,
 		if (zram_get_priority(zram, index) + 1 >= prio_max)
 			goto next;
 
-		pps->index = index;
-		place_pp_slot(zram, ctl, pps);
-		pps = NULL;
+		ok = place_pp_slot(zram, ctl, index);
 next:
 		zram_slot_unlock(zram, index);
+		if (!ok)
+			break;
 	}
 
-	kfree(pps);
 	return 0;
 }
 
-- 
2.48.1.658.g4767266eb4-goog