Messages in this thread | | | Subject | Re: [PATCH] zswap: Add shrink_enabled that can disable swap shrink to increase store performance | From | Hui Zhu <> | Date | Mon, 11 Nov 2019 09:57:53 +0800 |
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On 2019/11/9 12:04 上午, Dan Streetman wrote: > On Fri, Oct 25, 2019 at 4:02 AM Hui Zhu <teawaterz@linux.alibaba.com> 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?
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@linux.alibaba.com> >> --- >> 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 >>
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