Hi Andrew,
On Mon, Feb 06, 2017 at 12:16:44AM +0900, Minchan Kim wrote:
> From: zhouxianrong <zhouxianr...@huawei.com>
>
> the idea is that without doing more calculations we extend zero pages
> to same element pages for zram. zero page is special case of
> same element page with zero element.
>
> 1. the test is done under android 7.0
> 2. startup too many applications circularly
> 3. sample the zero pages, same pages (none-zero element)
> and total pages in function page_zero_filled
>
> the result is listed as below:
>
> ZERO SAME TOTAL
> 36214 17842 598196
>
> ZERO/TOTAL SAME/TOTAL (ZERO+SAME)/TOTAL ZERO/SAME
> AVERAGE 0.060631909 0.024990816 0.085622726
> 2.663825038
> STDEV 0.00674612 0.005887625 0.009707034 2.115881328
> MAX 0.069698422 0.030046087 0.094975336
> 7.56043956
> MIN 0.03959586 0.007332205 0.056055193
> 1.928985507
>
> from above data, the benefit is about 2.5% and up to 3% of total
> swapout pages.
>
> the defect of the patch is that when we recovery a page from
> non-zero element the operations are low efficient for partial
> read.
>
> This patch extend zero_page to same_page so if there is any user to have
> monitored zero_pages, he will be surprised if the number is increased
> but it's no harmful, I believe.
>
> Link:
> http://lkml.kernel.org/r/1483692145-75357-1-git-send-email-zhouxianr...@huawei.com
> Signed-off-by: zhouxianrong <zhouxianr...@huawei.com>
> Signed-off-by: Minchan Kim <minc...@kernel.org>
zhouxianrong pointed out we shouldn't free same element pages in zram_meta_free.
Otherwise, it can encounter oops due to invalid handle passed into zram_free.
This patch fixes it. Please fold this patch into
zram-extend-zero-pages-to-same-element-pages.patch.
Thanks.
>From e5a2a1dac4783f29d028170724578c0d11c80975 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minc...@kernel.org>
Date: Tue, 7 Feb 2017 12:00:05 +0900
Subject: [PATCH] zram: do not free same element pages in zram_meta_free
zhouxianrong pointed out that we shouldn't free same element pages
in zram_meta_free. Otherwise, it will encounter oops due to invalid
handle value.
Signed-off-by: Minchan Kim <minc...@kernel.org>
---
Andrew,
Please fold it to zram-extend-zero-pages-to-same-element-pages.patch.
Thanks.
drivers/block/zram/zram_drv.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index c20b05a84f21..a25d34a8af19 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -425,8 +425,11 @@ static void zram_meta_free(struct zram_meta *meta, u64
disksize)
/* Free all pages that are still in this zram device */
for (index = 0; index < num_pages; index++) {
unsigned long handle = meta->table[index].handle;
-
- if (!handle)
+ /*
+ * No memory is allocated for same element filled pages.
+ * Simply clear same page flag.
+ */
+ if (!handle || zram_test_flag(meta, index, ZRAM_SAME))
continue;
zs_free(meta->mem_pool, handle);
--
2.7.4
