+ zram-dont-retry-compress-incompressible-page.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: zram: don't retry compress incompressible page
has been added to the -mm mm-unstable branch.  Its filename is
     zram-dont-retry-compress-incompressible-page.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-dont-retry-compress-incompressible-page.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Alexey Romanov <avromanov@sberdevices.ru>
Subject: zram: don't retry compress incompressible page
Date: Wed, 10 Aug 2022 14:28:57 +0300

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/20220810112857.90278-1-avromanov@sberdevices.ru
Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/block/zram/zram_drv.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

--- a/drivers/block/zram/zram_drv.c~zram-dont-retry-compress-incompressible-page
+++ a/drivers/block/zram/zram_drv.c
@@ -1410,9 +1410,20 @@ 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);
_

Patches currently in -mm which might be from avromanov@sberdevices.ru are

zsmalloc-zs_object_copy-add-clarifying-comment.patch
zsmalloc-remove-unnecessary-size_class-null-check.patch
zsmalloc-zs_object_copy-replace-email-link-to-doc.patch
zram-dont-retry-compress-incompressible-page.patch