Hi Chao, On Thu, Aug 25, 2016 at 05:22:29PM +0800, Chao Yu wrote: > Hi Jaegeuk, > > On 2016/8/24 0:53, Jaegeuk Kim wrote: > > Hi Chao, > > > > On Sun, Aug 21, 2016 at 11:21:30PM +0800, Chao Yu wrote: > >> From: Chao Yu <yuch...@huawei.com> > >> > >> In batch discard approach of fstrim will grab/release gc_mutex lock > >> repeatly, it makes contention of the lock becoming more intensive. > >> > >> So after one batch discards were issued in checkpoint and the lock > >> was released, it's better to do schedule() to increase opportunity > >> of grabbing gc_mutex lock for other competitors. > >> > >> Signed-off-by: Chao Yu <yuch...@huawei.com> > >> --- > >> fs/f2fs/segment.c | 2 ++ > >> 1 file changed, 2 insertions(+) > >> > >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > >> index 020767c..d0f74eb 100644 > >> --- a/fs/f2fs/segment.c > >> +++ b/fs/f2fs/segment.c > >> @@ -1305,6 +1305,8 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct > >> fstrim_range *range) > >> mutex_unlock(&sbi->gc_mutex); > >> if (err) > >> break; > >> + > >> + schedule(); > > > > Hmm, if other thread is already waiting for gc_mutex, we don't need this > > here. > > In order to avoid long latency, wouldn't it be enough to reduce the batch > > size? > > Hmm, when fstrim call mutex_unlock we will pop one blocked locker from FIFO > list > of mutex lock, and wake it up, then fstrimer will try to lock gc_mutex for > next > batch trim, so the popped locker and fstrimer will make a new competition in > gc_mutex.
Before trying to grab gc_mutex by fstrim again, there are already blocked tasks waiting for gc_mutex. Hence the next one should be selectec by FIFO, no? Thanks, > If fstrimer is running in a big core, and popped locker is running in > a small core, we can't guarantee popped locker can win the race, and for the > most of time, fstrimer will win. So in order to reduce starvation of other > gc_mutext locker, it's better to do schedule() here. > > Thanks, > > > > > Thanks, > > > >> } > >> out: > >> range->len = F2FS_BLK_TO_BYTES(cpc.trimmed); > >> -- > >> 2.7.2 > > > > . > >
