| Message ID | CAEemH2c=EWHb1Ua6Fe4g_kF2JC8LKoiySPabZ7xXF43ovrNFmg@mail.gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, May 29, 2018 at 10:57 PM, Li Wang <liwang@redhat.com> wrote: > Hi Dan, > > On Wed, May 30, 2018 at 5:14 AM, Dan Streetman <ddstreet@ieee.org> wrote: >> >> 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. > > > Sorry for that confusing, I am a pretty new to zswap. > > To specify 0 to max_pool_percent is purpose to verify if zswap stopping work > when there is no space in compressed pool. > > Another consideration from me is: > > [Method A] > > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -1021,7 +1021,7 @@ static int zswap_frontswap_store(unsigned type, > pgoff_t offset, > /* reclaim space if needed */ > if (zswap_is_full()) { > zswap_pool_limit_hit++; > - if (zswap_shrink()) { > + if (!zswap_max_pool_percent || zswap_shrink()) { > zswap_reject_reclaim_fail++; > ret = -ENOMEM; > goto reject; > > This make sure the compressed pool is enough to do zswap_shrink(). > > >> >> >> 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). >> > > Ok, it sounds like can also fix the issue. The changes maybe like: > > [Method B] > > --- 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; > + } > } > > > So, which one do you think is better, A or B? this is better. > > -- > Regards, > Li Wang
--- a/mm/zswap.c +++ b/mm/zswap.c @@ -1021,7 +1021,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, /* reclaim space if needed */ if (zswap_is_full()) { zswap_pool_limit_hit++; - if (zswap_shrink()) { + if (!zswap_max_pool_percent || zswap_shrink()) { zswap_reject_reclaim_fail++; ret = -ENOMEM; goto reject; This make sure the compressed pool is enough to do zswap_shrink(). > > 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). > > Ok, it sounds like can also fix the issue. The changes maybe like: [Method B] --- 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; + } }