linux-kernel - [PATCH v1] zram: don't retry compress incompressible page

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Date:   Fri, 22 Apr 2022 14:59:59 +0300
From:   Alexey Romanov <avromanov@...rdevices.ru>
To:     <minchan@...nel.org>, <ngupta@...are.org>,
        <senozhatsky@...omium.org>, <linux-block@...r.kernel.org>
CC:     <axboe@...omium.org>, <kernel@...rdevices.ru>,
        <linux-kernel@...r.kernel.org>, <mnitenko@...il.com>,
        Alexey Romanov <avromanov@...rdevices.ru>,
        Dmitry Rokosov <ddrokosov@...rdevices.ru>
Subject: [PATCH v1] 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.

Signed-off-by: Alexey Romanov <avromanov@...rdevices.ru>
Signed-off-by: Dmitry Rokosov <ddrokosov@...rdevices.ru>
---
 drivers/block/zram/zram_drv.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index cb253d80d72b..bb9dd8b64176 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1413,9 +1413,20 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 		handle = zs_malloc(zram->mem_pool, comp_len,
 				GFP_NOIO | __GFP_HIGHMEM |
 				__GFP_MOVABLE);
-		if (handle)
+		if (!handle)
+			return -ENOMEM;
+
+		if (comp_len != PAGE_SIZE)
 			goto compress_again;
-		return -ENOMEM;
+
+		/*
+		 * 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);
-- 
2.30.1