4.4-stable review patch. If anyone has any objections, please let me know.
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From: Li Wang liwang@redhat.com
[ Upstream commit 16e536ef47f567289a5699abee9ff7bb304bc12d ]
/sys/../zswap/stored_pages keeps rising in a zswap test with "zswap.max_pool_percent=0" parameter. But it should not compress or store pages any more since there is no space in the compressed pool.
Reproduce steps: 1. Boot kernel with "zswap.enabled=1" 2. Set the max_pool_percent to 0 # echo 0 > /sys/module/zswap/parameters/max_pool_percent 3. Do memory stress test to see if some pages have been compressed # stress --vm 1 --vm-bytes $mem_available"M" --timeout 60s 4. Watching the 'stored_pages' number increasing or not
The root cause is:
When zswap_max_pool_percent is set to 0 via kernel parameter, zswap_is_full() will always return true due to zswap_shrink(). But if the shinking is able to reclain a page successfully the code then proceeds to compressing/storing another page, so the value of stored_pages will keep changing.
To solve the issue, this patch adds a zswap_is_full() check again after zswap_shrink() to make sure it's now under the max_pool_percent, and to not compress/store if we reached the limit.
Link: http://lkml.kernel.org/r/20180530103936.17812-1-liwang@redhat.com Signed-off-by: Li Wang liwang@redhat.com Acked-by: Dan Streetman ddstreet@ieee.org Cc: Seth Jennings sjenning@redhat.com Cc: Huang Ying huang.ying.caritas@gmail.com Cc: Yu Zhao yuzhao@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/zswap.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/mm/zswap.c +++ b/mm/zswap.c @@ -1018,6 +1018,15 @@ static int zswap_frontswap_store(unsigne ret = -ENOMEM; goto reject; } + + /* A second zswap_is_full() check after + * zswap_shrink() to make sure it's now + * under the max_pool_percent + */ + if (zswap_is_full()) { + ret = -ENOMEM; + goto reject; + } }
/* allocate entry */