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SubjectRe: [PATCH v2] zswap: re-check zswap_is_full after do zswap_shrink
On Wed, May 30, 2018 at 6:39 AM, Li Wang <liwang@redhat.com> wrote:
> The '/sys/../zswap/stored_pages:' keep raising in zswap test with
> "zswap.max_pool_percent=0" parameter. But theoretically, it should
> not compress or store pages any more since there is no space in
> 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 setting to 0 via kernel parameter, the
> zswap_is_full() will always return true to do zswap_shrink(). But if
> the shinking is able to reclain a page successful, then proceeds to
> compress/store another page, so the value of stored_pages will keep
> changing.
>
> To solve the issue, this patch adds zswap_is_full() check again after
> zswap_shrink() to make sure it's now under the max_pool_percent, and
> not to compress/store if reach its limitaion.
>
> Signed-off-by: Li Wang <liwang@redhat.com>

Acked-by: Dan Streetman <ddstreet@ieee.org>

> Cc: Seth Jennings <sjenning@redhat.com>
> Cc: Dan Streetman <ddstreet@ieee.org>
> Cc: Huang Ying <huang.ying.caritas@gmail.com>
> Cc: Yu Zhao <yuzhao@google.com>
> ---
> mm/zswap.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 61a5c41..fd320c3 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1026,6 +1026,15 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> 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 */
> --
> 2.9.5
>

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