zram: move post-processing target allocation

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.

Link: https://lkml.kernel.org/r/20250303022425.285971-12-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index bb88b63d193b6bd28a32f9fecb5cd87a8b7b14f6..f6e887f94b71ab8d8a73eeb79b3140c3188a05f3 100644 (file)
--- 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;
 }