zsmalloc: do not scan for allocated objects in empty zspage

Patch series "zsmalloc: small compaction improvements", v2.

A tiny series that can reduce the number of find_alloced_obj() invocations
(which perform a linear scan of sub-page) during compaction.  Inspired by
Alexey Romanov's findings.

This patch (of 3):

zspage migration can terminate as soon as it moves the last allocated
object from the source zspage.  Add a simple helper zspage_empty() that
tests zspage ->inuse on each migration iteration.

Link: https://lkml.kernel.org/r/20230624053120.643409-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Suggested-by: Alexey Romanov <AVRomanov@sberdevices.ru>
Reviewed-by: Alexey Romanov <avromanov@sberdevices.ru>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 3f057970504e3b061242b9f2de65c42357fea5f4..5d60eaedc3b79414f7fb9eb32fb5f7f849bf37a8 100644 (file)
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1147,6 +1147,11 @@ static bool zspage_full(struct size_class *class, struct zspage *zspage)
        return get_zspage_inuse(zspage) == class->objs_per_zspage;
 }
 
+static bool zspage_empty(struct zspage *zspage)
+{
+       return get_zspage_inuse(zspage) == 0;
+}
+
 /**
  * zs_lookup_class_index() - Returns index of the zsmalloc &size_class
  * that hold objects of the provided size.
@@ -1625,6 +1630,10 @@ static void migrate_zspage(struct zs_pool *pool, struct size_class *class,
                obj_idx++;
                record_obj(handle, free_obj);
                obj_free(class->size, used_obj);
+
+               /* Stop if there are no more objects to migrate */
+               if (zspage_empty(get_zspage(s_page)))
+                       break;
        }
 
        /* Remember last position in this iteration */