On Sun, Nov 10, 2019 at 8:58 PM Hui Zhu <teawaterz@xxxxxxxxxxxxxxxxx> wrote: > > > > On 2019/11/9 12:04 上午, Dan Streetman wrote: > > On Fri, Oct 25, 2019 at 4:02 AM Hui Zhu <teawaterz@xxxxxxxxxxxxxxxxx> wrote: > >> > >> zswap will try to shrink pool when zswap is full. > >> This commit add shrink_enabled that can disable swap shrink to increase > >> store performance. User can disable swap shrink if care about the store > >> performance. > > > > I don't understand - if zswap is full it can't store any more pages > > without shrinking the current pool. This commit will just force all > > pages to swap when zswap is full. This has nothing to do with 'store > > performance'. > > > > I think it would be much better to remove any user option for this and > > implement some hysteresis; store pages normally until the zpool is > > full, then reject all pages going to that pool until there is some % > > free, at which point allow pages to be stored into the pool again. > > That will prevent (or at least reduce) the constant performance hit > > when a zpool fills up, and just fallback to normal swapping to disk > > until the zpool has some amount of free space again. > > > > This idea is really cool! > Do you mind I make a patch for it? Sorry for the delay, again. I think Vitaly has a patch adding this. > > Thanks, > Hui > > >> > >> For example in a VM with 1 CPU 1G memory 4G swap: > >> echo lz4 > /sys/module/zswap/parameters/compressor > >> echo z3fold > /sys/module/zswap/parameters/zpool > >> echo 0 > /sys/module/zswap/parameters/same_filled_pages_enabled > >> echo 1 > /sys/module/zswap/parameters/enabled > >> usemem -a -n 1 $((4000 * 1024 * 1024)) > >> 4718592000 bytes / 114937822 usecs = 40091 KB/s > >> 101700 usecs to free memory > >> echo 0 > /sys/module/zswap/parameters/shrink_enabled > >> usemem -a -n 1 $((4000 * 1024 * 1024)) > >> 4718592000 bytes / 8837320 usecs = 521425 KB/s > >> 129577 usecs to free memory > >> > >> The store speed increased when zswap shrink disabled. > >> > >> Signed-off-by: Hui Zhu <teawaterz@xxxxxxxxxxxxxxxxx> > >> --- > >> mm/zswap.c | 7 +++++++ > >> 1 file changed, 7 insertions(+) > >> > >> diff --git a/mm/zswap.c b/mm/zswap.c > >> index 46a3223..731e3d1e 100644 > >> --- a/mm/zswap.c > >> +++ b/mm/zswap.c > >> @@ -114,6 +114,10 @@ static bool zswap_same_filled_pages_enabled = true; > >> module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled, > >> bool, 0644); > >> > >> +/* Enable/disable zswap shrink (enabled by default) */ > >> +static bool zswap_shrink_enabled = true; > >> +module_param_named(shrink_enabled, zswap_shrink_enabled, bool, 0644); > >> + > >> /********************************* > >> * data structures > >> **********************************/ > >> @@ -947,6 +951,9 @@ static int zswap_shrink(void) > >> struct zswap_pool *pool; > >> int ret; > >> > >> + if (!zswap_shrink_enabled) > >> + return -EPERM; > >> + > >> pool = zswap_pool_last_get(); > >> if (!pool) > >> return -ENOENT; > >> -- > >> 2.7.4 > >>
