zram: don't retry compress incompressible page

It doesn't make sense for us to retry to compress an uncompressible page
(comp_len == PAGE_SIZE) in zsmalloc slowpath, because we will be storing
it uncompressed anyway.  We can avoid wasting time on another compression
attempt.  It is enough to take lock (zcomp_stream_get) and execute the
code below.

Link: https://lkml.kernel.org/r/20220824113117.78849-1-avromanov@sberdevices.ru
Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Alexey Romanov <avromanov@sberdevices.ru>
Cc: Dmitry Rokosov <DDRokosov@sberdevices.ru>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
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 add43f6..607f463 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1410,9 +1410,19 @@ compress_again:
                handle = zs_malloc(zram->mem_pool, comp_len,
                                GFP_NOIO | __GFP_HIGHMEM |
                                __GFP_MOVABLE);
-               if (!IS_ERR((void *)handle))
+               if (IS_ERR((void *)handle))
+                       return PTR_ERR((void *)handle);
+
+               if (comp_len != PAGE_SIZE)
                        goto compress_again;
-               return PTR_ERR((void *)handle);
+               /*
+                * If the page is not compressible, you need to acquire the lock and
+                * execute the code below. The zcomp_stream_get() call is needed to
+                * disable the cpu hotplug and grab the zstrm buffer back.
+                * It is necessary that the dereferencing of the zstrm variable below
+                * occurs correctly.
+                */
+               zstrm = zcomp_stream_get(zram->comp);
        }
 
        alloced_pages = zs_get_total_pages(zram->mem_pool);