linux-kernel - [PATCH] [staging][zram] Fix handling of incompressible pages

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Message-Id: <1349746364-8051-1-git-send-email-ngupta@vflare.org>
Date:	Mon,  8 Oct 2012 18:32:44 -0700
From:	Nitin Gupta <ngupta@...are.org>
To:	Greg KH <greg@...ah.com>
Cc:	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Sam Hansen <solid.se7en@...il.com>,
	Linux Driver Project <devel@...uxdriverproject.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] [staging][zram] Fix handling of incompressible pages

Change 130f315a introduced a bug in the handling of incompressible
pages which resulted in memory allocation failure for such pages.
The fix is to store the page as-is i.e. without compression if the
compressed size exceeds a threshold (max_zpage_size) and request
exactly PAGE_SIZE sized buffer from zsmalloc.

Signed-off-by: Nitin Gupta <ngupta@...are.org>
Reported-by: viechweg@...il.com
Reported-by: paerley@...il.com
Reported-by: wu.tommy@...il.com
Tested-by: wu.tommy@...il.com
Tested-by: michael@...elder.org
---
 drivers/staging/zram/zram_drv.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 653b074..6edefde 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -223,8 +223,13 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	cmem = zs_map_object(zram->mem_pool, zram->table[index].handle,
 				ZS_MM_RO);
 
-	ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
+	if (zram->table[index].size == PAGE_SIZE) {
+		memcpy(uncmem, cmem, PAGE_SIZE);
+		ret = LZO_E_OK;
+	} else {
+		ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
 				    uncmem, &clen);
+	}
 
 	if (is_partial_io(bvec)) {
 		memcpy(user_mem + bvec->bv_offset, uncmem + offset,
@@ -342,8 +347,11 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		goto out;
 	}
 
-	if (unlikely(clen > max_zpage_size))
+	if (unlikely(clen > max_zpage_size)) {
 		zram_stat_inc(&zram->stats.bad_compress);
+		src = uncmem;
+		clen = PAGE_SIZE;
+	}
 
 	handle = zs_malloc(zram->mem_pool, clen);
 	if (!handle) {
-- 
1.7.9.5

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