| Message ID | 20180524095752.17770-1-liwang@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, May 24, 2018 at 5:57 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 for > compressed pool. > > Reproduce steps: > > 1. Boot kernel with "zswap.enabled=1 zswap.max_pool_percent=17" > 2. Set the max_pool_percent to 0 > # echo 0 > /sys/module/zswap/parameters/max_pool_percent > Confirm this parameter works fine > # cat /sys/kernel/debug/zswap/pool_total_size > 0 > 3. Do memory stress test to see if some pages have been compressed > # stress --vm 1 --vm-bytes $mem_available"M" --timeout 60s > Watching the 'stored_pages' numbers increasing or not > > The root cause is: > > When the zswap_max_pool_percent is set to 0 via kernel parameter, the zswap_is_full() > will always return true to shrink the pool size by zswap_shrink(). If the pool size > has been shrinked a little success, zswap will do compress/store pages again. Then we > get fails on that as above. special casing 0% doesn't make a lot of sense to me, and I'm not entirely sure what exactly you are trying to fix here. however, zswap does currently do a zswap_is_full() check, and then if it's able to reclaim a page happily proceeds to store another page, without re-checking zswap_is_full(). If you're trying to fix that, then I would ack a patch that adds a second zswap_is_full() check after zswap_shrink() to make sure it's now under the max_pool_percent (or somehow otherwise fixes that behavior). > > Signed-off-by: Li Wang <liwang@redhat.com> > 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 | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 61a5c41..2b537bb 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -1007,6 +1007,11 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, > u8 *src, *dst; > struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) }; > > + if (!zswap_max_pool_percent) { > + ret = -ENOMEM; > + goto reject; > + } > + > /* THP isn't supported */ > if (PageTransHuge(page)) { > ret = -EINVAL; > -- > 2.9.5 >
diff --git a/mm/zswap.c b/mm/zswap.c index 61a5c41..2b537bb 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -1007,6 +1007,11 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, u8 *src, *dst; struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) }; + if (!zswap_max_pool_percent) { + ret = -ENOMEM; + goto reject; + } + /* THP isn't supported */ if (PageTransHuge(page)) { ret = -EINVAL;
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 for compressed pool. Reproduce steps: 1. Boot kernel with "zswap.enabled=1 zswap.max_pool_percent=17" 2. Set the max_pool_percent to 0 # echo 0 > /sys/module/zswap/parameters/max_pool_percent Confirm this parameter works fine # cat /sys/kernel/debug/zswap/pool_total_size 0 3. Do memory stress test to see if some pages have been compressed # stress --vm 1 --vm-bytes $mem_available"M" --timeout 60s Watching the 'stored_pages' numbers increasing or not The root cause is: When the zswap_max_pool_percent is set to 0 via kernel parameter, the zswap_is_full() will always return true to shrink the pool size by zswap_shrink(). If the pool size has been shrinked a little success, zswap will do compress/store pages again. Then we get fails on that as above. Signed-off-by: Li Wang <liwang@redhat.com> 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 | 5 +++++ 1 file changed, 5 insertions(+)