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. 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 > > . >
