From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chao Yu Subject: Re: [PATCH 2/3] f2fs: schedule in between two continous batch discards Date: Thu, 25 Aug 2016 17:22:29 +0800 Message-ID: References: <1471792891-2388-1-git-send-email-chao@kernel.org> <1471792891-2388-2-git-send-email-chao@kernel.org> <20160823165353.GA73835@jaegeuk> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160823165353.GA73835@jaegeuk> Sender: linux-kernel-owner@vger.kernel.org To: Jaegeuk Kim , Chao Yu Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org List-Id: linux-f2fs-devel.lists.sourceforge.net 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 >> >> 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 >> --- >> 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 > > . > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932322AbcHYJWr (ORCPT ); Thu, 25 Aug 2016 05:22:47 -0400 Received: from szxga03-in.huawei.com ([119.145.14.66]:6031 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755623AbcHYJWp (ORCPT ); Thu, 25 Aug 2016 05:22:45 -0400 Subject: Re: [PATCH 2/3] f2fs: schedule in between two continous batch discards To: Jaegeuk Kim , Chao Yu References: <1471792891-2388-1-git-send-email-chao@kernel.org> <1471792891-2388-2-git-send-email-chao@kernel.org> <20160823165353.GA73835@jaegeuk> CC: , From: Chao Yu Message-ID: Date: Thu, 25 Aug 2016 17:22:29 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <20160823165353.GA73835@jaegeuk> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090201.57BEB8DD.0057,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-05-26 15:14:31, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 3d9dcc267003830bc9051c2815de0067 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >> >> 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 >> --- >> 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 > > . >