Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Hi,
2013/9/11 Chao Yu
>
> Hi Kim,
>
> I did some tests as you mention of using random instead of spin_lock.
> The test model is as following:
> eight threads race to grab one of eight locks for one thousand times,
> and I used four methods to generate lock num:
>
> 1.atomic_add_return(1, &sbi->next_lock_num) % NR_GLOBAL_LOCKS;
> 2.spin_lock(); next_lock_num++ % NR_GLOBAL_LOCKS; spin_unlock();
> 3.ktime_get().tv64 % NR_GLOBAL_LOCKS;
> 4.get_random_bytes(&next_lock, sizeof(unsigned int));
>
> the result indicate that:
> max count of collide continuously: 4 > 3 > 2 = 1
> max-min count of lock is grabbed: 4 > 3 > 2 = 1
> elapsed time of generating: 3 > 2 > 4 > 1
>
> So I think it's better to use atomic_add_return in round-robin method to
> cost less time and reduce collide.
> What's your opinion?
Could you test with sbi->next_lock_num++ only instead of using
atomic_add_return?
IMO, this is just an integer value and still I don't think this value should
be covered by any kind of locks.
Thanks,
>
> thanks
>
> --- Original Message ---
> Sender : ??? S5(??)/??/?(???)/
> Date : 九月 10, 2013 09:52 (GMT+09:00)
> Title : Re: [f2fs-dev][PATCH] f2fs: optimize fs_lock for better performance
>
> Hi,
>
> At first, thank you for the report and please follow the email writing
> rules. :)
>
> Anyway, I agree to the below issue.
> One thing that I can think of is that we don't need to use the
> spin_lock, since we don't care about the exact lock number, but just
> need to get any not-collided number.
>
> So, how about removing the spin_lock?
> And how about using a random number?
> Thanks,
>
> 2013-09-06 (?), 09:48 +, Chao Yu:
> > Hi Kim:
> >
> > I think there is a performance problem: when all sbi->fs_lock is
> > holded,
> >
> > then all other threads may get the same next_lock value from
> > sbi->next_lock_num in function mutex_lock_op,
> >
> > and wait to get the same lock at position fs_lock[next_lock], it
> > unbalance the fs_lock usage.
> >
> > It may lost performance when we do the multithread test.
> >
> >
> >
> > Here is the patch to fix this problem:
> >
> >
> >
> > Signed-off-by: Yu Chao
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >
> > old mode 100644
> >
> > new mode 100755
> >
> > index 467d42d..983bb45
> >
> > --- a/fs/f2fs/f2fs.h
> >
> > +++ b/fs/f2fs/f2fs.h
> >
> > @@ -371,6 +371,7 @@ struct f2fs_sb_info {
> >
> > struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
> > operations */
> >
> > struct mutex node_write;/* locking node writes
> > */
> >
> > struct mutex writepages;/* mutex for
> > writepages() */
> >
> > + spinlock_t spin_lock; /* lock for
> > next_lock_num */
> >
> > unsigned char next_lock_num;/* round-robin global
> > locks */
> >
> > int por_doing; /* recovery is doing
> > or not */
> >
> > int on_build_free_nids; /* build_free_nids is
> > doing */
> >
> > @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
> > f2fs_sb_info *sbi)
> >
> >
> >
> > static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
> >
> > {
> >
> > - unsigned char next_lock = sbi->next_lock_num %
> > NR_GLOBAL_LOCKS;
> >
> > + unsigned char next_lock;
> >
> > int i = 0;
> >
> >
> >
> > for (; i < NR_GLOBAL_LOCKS; i++)
> >
> > if (mutex_trylock(&sbi->fs_lock[i]))
> >
> > return i;
> >
> >
> >
> > - mutex_lock(&sbi->fs_lock[next_lock]);
> >
> > + spin_lock(&sbi->spin_lock);
> >
> > + next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
> >
> > sbi->next_lock_num++;
> >
> > + spin_unlock(&sbi->spin_lock);
> >
> > +
> >
> > + mutex_lock(&sbi->fs_lock[next_lock]);
> >
> > return next_lock;
> >
> > }
> >
> >
> >
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >
> > old mode 100644
> >
> > new mode 100755
> >
> > index 75c7dc3..4f27596
> >
> > --- a/fs/f2fs/super.c
> >
> > +++ b/fs/f2fs/super.c
> >
> > @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block *sb,
> > void *data, int silent)
> >
> > mutex_init(&sbi->cp_mutex);
> >
> > for (i = 0; i < NR_GLOBAL_LOCKS; i++)
> >
> > mutex_init(&sbi->fs_lock[i]);
> >
> > + spin_lock_init(&sbi->spin_lock);
> >
> > mutex_init(&sbi->node_write);
> >
> > sbi->por_doing = 0;
> >
> > spin_lock_init(&sbi->stat_lock);
> >
> > (END)
> >
> >
> >
> >
> >
> >
>
> --
> Jaegeuk Kim
> Samsung
--
How ServiceNow helps IT people transform IT departments:
1. Consolidate legacy IT systems to a single system of record for IT
2. Standardize and globalize service processes across IT
3. Implement zero-touch automation to replace manual, redundant tasks
http://pubads.g.doubleclick.net/gampad/clk?id=5127&iu=/4140/ostg.clktrk
Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Hi Russ,
The usage of fs_locks is for the recovery, so it doesn't matter
with stress-testing.
Actually what I've concerned is that we should not grab two or
more fs_locks in the same call path.
Thanks,
2013/9/11 Russ Knize :
> Hi Jaegeuk/Gu,
>
> I've removed the lock and have been stress-testing with SELinux and some
> additional xattr torture for 24+ hours. I have not encountered any issues
> yet.
>
> My previous suggestion about moving the lock is probably not a good idea
> without some significant code rework (thanks to the f2fs_balance_fs call in
> f2fs_setxattr).
>
> Russ
>
> On Tue, Sep 10, 2013 at 10:22 PM, Gu Zheng wrote:
>>
>> Hi Jaegeuk,
>> On 09/10/2013 08:59 AM, Jaegeuk Kim wrote:
>>
>> > Hi,
>> >
>> > 2013-09-07 (토), 08:00 +, Chao Yu:
>> >> Hi Knize,
>> >>
>> >> Thanks for your reply, I think it's actually meaningless that it's
>> >> being named after "spin_lock",
>> >> it's better to rename this spinlock to "round_robin_lock".
>> >>
>> >> This patch can only resolve the issue of unbalanced fs_lock usage,
>> >> it can not fix the deadlock issue.
>> >> can we fix deadlock issue through this method:
>> >>
>> >> - vfs_create()
>> >> - f2fs_create() - takes an fs_lock and save current thread info into
>> >> thread_info[NR_GLOBAL_LOCKS]
>> >> - f2fs_add_link()
>> >>- __f2fs_add_link()
>> >> - init_inode_metadata()
>> >> - f2fs_init_security()
>> >> - security_inode_init_security()
>> >>- f2fs_initxattrs()
>> >> - f2fs_setxattr() - get fs_lock only if there is no current
>> >> thread info in thread_info
>> >>
>> >> So it keeps one thread can only hold one fs_lock to avoid deadlock.
>> >> Can we use this solution?
>> >
>> > It could be.
>> > But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs()
>>
>> Agree. This fs_lock here is used to protect the xattr from parallel
>> modification,
>> but here is in the initxattrs routine, parallel modification can not
>> happen.
>> And in the normal setxattr routine the inode->i_mutex (vfs layer) is used
>> to
>> avoid parallel modification. So I think this fs_lock is needless.
>> Am I missing something?
>>
>> Regards,
>> Gu
>>
>> > level, since this case only happens when f2fs_initxattrs() is called.
>> > Let's think about ut in more detail.
>> > Thanks,
>> >
>> >>
>> >>
>> >>
>> >> thanks again!
>> >>
>> >>
>> >>
>> >> --- Original Message ---
>> >>
>> >> Sender : Russ Knize
>> >>
>> >> Date : 九月 07, 2013 04:25 (GMT+09:00)
>> >>
>> >> Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better
>> >> performance
>> >>
>> >>
>> >>
>> >> I encountered this same issue recently and solved it in much the same
>> >> way. Can we rename "spin_lock" to something more meaningful?
>> >>
>> >>
>> >> This race actually exposed a potential deadlock between f2fs_create()
>> >> and f2fs_initxattrs():
>> >>
>> >>
>> >> - vfs_create()
>> >> - f2fs_create() - takes an fs_lock
>> >> - f2fs_add_link()
>> >>- __f2fs_add_link()
>> >> - init_inode_metadata()
>> >> - f2fs_init_security()
>> >> - security_inode_init_security()
>> >>- f2fs_initxattrs()
>> >> - f2fs_setxattr() - also takes an fs_lock
>> >>
>> >>
>> >> If another CPU happens to have the same lock that f2fs_setxattr() was
>> >> trying to take because of the race around next_lock_num, we can get
>> >> into a deadlock situation if the two threads are also contending over
>> >> another resource (like bdi).
>> >>
>> >>
>> >> Another scenario is if the above happens while another thread is in
>> >> the middle of grabbing all of the locks via mutex_lock_all().
>> >> f2fs_create() is holding a lock that mutex_lock_all() is waiting for
>> >> and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting
>> >> for.
>> >>
>> >>
>> >> Russ
>> >>
>> >>
>> >> On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu wrote:
>> >> Hi Kim:
>> >>
>> >> I think there is a performance problem: when all
>> >> sbi->fs_lock is holded,
>> >>
>> >> then all other threads may get the same next_lock value from
>> >> sbi->next_lock_num in function mutex_lock_op,
>> >>
>> >> and wait to get the same lock at position fs_lock[next_lock],
>> >> it unbalance the fs_lock usage.
>> >>
>> >> It may lost performance when we do the multithread test.
>> >>
>> >>
>> >>
>> >> Here is the patch to fix this problem:
>> >>
>> >>
>> >>
>> >> Signed-off-by: Yu Chao
>> >>
>> >> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> >>
>> >> old mode 100644
>> >>
>> >> new mode 100755
>> >>
>> >> index 467d42d..983bb45
>> >>
>> >> --- a/fs/f2fs/f2fs.h
>> >>
>> >> +++ b/fs/f2fs/f2fs.h
>> >>
>> >> @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>> >>
>> >> struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
>> >> operations */
>> >>
>> >> struct mutex node_write;/* locking
>>
Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Hi Gu,
2013/9/11 Gu Zheng :
> Hi Jaegeuk, Chao,
>
> On 09/10/2013 08:52 AM, Jaegeuk Kim wrote:
>
>> Hi,
>>
>> At first, thank you for the report and please follow the email writing
>> rules. :)
>>
>> Anyway, I agree to the below issue.
>> One thing that I can think of is that we don't need to use the
>> spin_lock, since we don't care about the exact lock number, but just
>> need to get any not-collided number.
>
> IMHO, just moving sbi->next_lock_num++ before
> mutex_lock(&sbi->fs_lock[next_lock])
> can avoid unbalance issue mostly.
> IMO, the case two or more threads increase sbi->next_lock_num in the same
> time is
> really very very little. If you think it is not rigorous, change
> next_lock_num to
> atomic one can fix it.
> What's your opinion?
As your opinion, I think it is enough to replace it with simple
sbi->next_lock_num++.
Thanks,
>
> Regards,
> Gu
>
>>
>> So, how about removing the spin_lock?
>> And how about using a random number?
>
>> Thanks,
>>
>> 2013-09-06 (금), 09:48 +, Chao Yu:
>>> Hi Kim:
>>>
>>> I think there is a performance problem: when all sbi->fs_lock is
>>> holded,
>>>
>>> then all other threads may get the same next_lock value from
>>> sbi->next_lock_num in function mutex_lock_op,
>>>
>>> and wait to get the same lock at position fs_lock[next_lock], it
>>> unbalance the fs_lock usage.
>>>
>>> It may lost performance when we do the multithread test.
>>>
>>>
>>>
>>> Here is the patch to fix this problem:
>>>
>>>
>>>
>>> Signed-off-by: Yu Chao
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>
>>> old mode 100644
>>>
>>> new mode 100755
>>>
>>> index 467d42d..983bb45
>>>
>>> --- a/fs/f2fs/f2fs.h
>>>
>>> +++ b/fs/f2fs/f2fs.h
>>>
>>> @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>>>
>>> struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
>>> operations */
>>>
>>> struct mutex node_write;/* locking node writes
>>> */
>>>
>>> struct mutex writepages;/* mutex for
>>> writepages() */
>>>
>>> + spinlock_t spin_lock; /* lock for
>>> next_lock_num */
>>>
>>> unsigned char next_lock_num;/* round-robin global
>>> locks */
>>>
>>> int por_doing; /* recovery is doing
>>> or not */
>>>
>>> int on_build_free_nids; /* build_free_nids is
>>> doing */
>>>
>>> @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
>>> f2fs_sb_info *sbi)
>>>
>>>
>>>
>>> static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
>>>
>>> {
>>>
>>> - unsigned char next_lock = sbi->next_lock_num %
>>> NR_GLOBAL_LOCKS;
>>>
>>> + unsigned char next_lock;
>>>
>>> int i = 0;
>>>
>>>
>>>
>>> for (; i < NR_GLOBAL_LOCKS; i++)
>>>
>>> if (mutex_trylock(&sbi->fs_lock[i]))
>>>
>>> return i;
>>>
>>>
>>>
>>> - mutex_lock(&sbi->fs_lock[next_lock]);
>>>
>>> + spin_lock(&sbi->spin_lock);
>>>
>>> + next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
>>>
>>> sbi->next_lock_num++;
>>>
>>> + spin_unlock(&sbi->spin_lock);
>>>
>>> +
>>>
>>> + mutex_lock(&sbi->fs_lock[next_lock]);
>>>
>>> return next_lock;
>>>
>>> }
>>>
>>>
>>>
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>
>>> old mode 100644
>>>
>>> new mode 100755
>>>
>>> index 75c7dc3..4f27596
>>>
>>> --- a/fs/f2fs/super.c
>>>
>>> +++ b/fs/f2fs/super.c
>>>
>>> @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block *sb,
>>> void *data, int silent)
>>>
>>> mutex_init(&sbi->cp_mutex);
>>>
>>> for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>>>
>>> mutex_init(&sbi->fs_lock[i]);
>>>
>>> + spin_lock_init(&sbi->spin_lock);
>>>
>>> mutex_init(&sbi->node_write);
>>>
>>> sbi->por_doing = 0;
>>>
>>> spin_lock_init(&sbi->stat_lock);
>>>
>>> (END)
>>>
>>>
>>>
>>>
>>>
>>>
>>
>
>
>
> --
> How ServiceNow helps IT people transform IT departments:
> 1. Consolidate legacy IT systems to a single system of record for IT
> 2. Standardize and globalize service processes across IT
> 3. Implement zero-touch automation to replace manual, redundant tasks
> http://pubads.g.doubleclick.net/gampad/clk?id=5127&iu=/4140/ostg.clktrk
> ___
> Linux-f2fs-devel mailing list
> Linux-f2fs-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
--
How ServiceNow helps IT people transform IT departments:
1. Consolidate legacy IT systems to a single system of record for IT
2. Standardize and globalize service processes across IT
3. Implement zero-touch automation to replace manual, redundant tasks
http://pubads.g.doubleclick.net/gampad/clk?id=5127&iu=/4140/ostg.clktrk
___
Linux-f2fs-deve
Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Jaegeuk, My tests include forced kernel panics while fsstress is running, which generates a lot of recovery activity. Sorry I wasn't more clear. I understand your concern, which is why I first tried to keep the fs_lock in the xattr_handler->set() path from VFS while removing it from the call path I shared earlier. Doing this requires reworking the xattr code a bit. Based on what Gu said about the inode mutex, it seems like we can just remove it. Russ On Wed, Sep 11, 2013 at 8:19 AM, Kim Jaegeuk wrote: > Hi Russ, > > The usage of fs_locks is for the recovery, so it doesn't matter > with stress-testing. > Actually what I've concerned is that we should not grab two or > more fs_locks in the same call path. > Thanks, > > 2013/9/11 Russ Knize : >> Hi Jaegeuk/Gu, >> >> I've removed the lock and have been stress-testing with SELinux and some >> additional xattr torture for 24+ hours. I have not encountered any issues >> yet. >> >> My previous suggestion about moving the lock is probably not a good idea >> without some significant code rework (thanks to the f2fs_balance_fs call in >> f2fs_setxattr). >> >> Russ >> >> On Tue, Sep 10, 2013 at 10:22 PM, Gu Zheng wrote: >>> >>> Hi Jaegeuk, >>> On 09/10/2013 08:59 AM, Jaegeuk Kim wrote: >>> >>> > Hi, >>> > >>> > 2013-09-07 (토), 08:00 +, Chao Yu: >>> >> Hi Knize, >>> >> >>> >> Thanks for your reply, I think it's actually meaningless that it's >>> >> being named after "spin_lock", >>> >> it's better to rename this spinlock to "round_robin_lock". >>> >> >>> >> This patch can only resolve the issue of unbalanced fs_lock usage, >>> >> it can not fix the deadlock issue. >>> >> can we fix deadlock issue through this method: >>> >> >>> >> - vfs_create() >>> >> - f2fs_create() - takes an fs_lock and save current thread info into >>> >> thread_info[NR_GLOBAL_LOCKS] >>> >> - f2fs_add_link() >>> >>- __f2fs_add_link() >>> >> - init_inode_metadata() >>> >> - f2fs_init_security() >>> >> - security_inode_init_security() >>> >>- f2fs_initxattrs() >>> >> - f2fs_setxattr() - get fs_lock only if there is no current >>> >> thread info in thread_info >>> >> >>> >> So it keeps one thread can only hold one fs_lock to avoid deadlock. >>> >> Can we use this solution? >>> > >>> > It could be. >>> > But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs() >>> >>> Agree. This fs_lock here is used to protect the xattr from parallel >>> modification, >>> but here is in the initxattrs routine, parallel modification can not >>> happen. >>> And in the normal setxattr routine the inode->i_mutex (vfs layer) is used >>> to >>> avoid parallel modification. So I think this fs_lock is needless. >>> Am I missing something? >>> >>> Regards, >>> Gu >>> >>> > level, since this case only happens when f2fs_initxattrs() is called. >>> > Let's think about ut in more detail. >>> > Thanks, >>> > >>> >> >>> >> >>> >> >>> >> thanks again! >>> >> >>> >> >>> >> >>> >> --- Original Message --- >>> >> >>> >> Sender : Russ Knize >>> >> >>> >> Date : 九月 07, 2013 04:25 (GMT+09:00) >>> >> >>> >> Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better >>> >> performance >>> >> >>> >> >>> >> >>> >> I encountered this same issue recently and solved it in much the same >>> >> way. Can we rename "spin_lock" to something more meaningful? >>> >> >>> >> >>> >> This race actually exposed a potential deadlock between f2fs_create() >>> >> and f2fs_initxattrs(): >>> >> >>> >> >>> >> - vfs_create() >>> >> - f2fs_create() - takes an fs_lock >>> >> - f2fs_add_link() >>> >>- __f2fs_add_link() >>> >> - init_inode_metadata() >>> >> - f2fs_init_security() >>> >> - security_inode_init_security() >>> >>- f2fs_initxattrs() >>> >> - f2fs_setxattr() - also takes an fs_lock >>> >> >>> >> >>> >> If another CPU happens to have the same lock that f2fs_setxattr() was >>> >> trying to take because of the race around next_lock_num, we can get >>> >> into a deadlock situation if the two threads are also contending over >>> >> another resource (like bdi). >>> >> >>> >> >>> >> Another scenario is if the above happens while another thread is in >>> >> the middle of grabbing all of the locks via mutex_lock_all(). >>> >> f2fs_create() is holding a lock that mutex_lock_all() is waiting for >>> >> and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting >>> >> for. >>> >> >>> >> >>> >> Russ >>> >> >>> >> >>> >> On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu wrote: >>> >> Hi Kim: >>> >> >>> >> I think there is a performance problem: when all >>> >> sbi->fs_lock is holded, >>> >> >>> >> then all other threads may get the same next_lock value from >>> >> sbi->next_lock_num in function mutex_lock_op, >>> >> >>> >> and wait to get the same lock at position fs_lock[next_lock], >>> >> it unbalance the fs_lock usage. >>> >> >>> >> It may lost performance when we do the m
Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Hi, On 11/09/2013 21:19, Kim Jaegeuk wrote: > Hi Russ, > > The usage of fs_locks is for the recovery, so it doesn't matter > with stress-testing. > Actually what I've concerned is that we should not grab two or > more fs_locks in the same call path. > Thanks, > I am wondering why we don't use other kind of methods like r/w semaphore instead of the fs_locks for access control purpose. Is it due to the little lower performance of r/w semaphore or other reasons? I think the r/w semaphore can bring more clearer access control over the current fs_locks, and will not suffer the problems reported here. It can be used in a way that i/o tasks just acquire read sem while the checkpoint task takes the write sem. Or do we have other better method? Regards, Jin > 2013/9/11 Russ Knize : >> Hi Jaegeuk/Gu, >> >> I've removed the lock and have been stress-testing with SELinux and some >> additional xattr torture for 24+ hours. I have not encountered any issues >> yet. >> >> My previous suggestion about moving the lock is probably not a good idea >> without some significant code rework (thanks to the f2fs_balance_fs call in >> f2fs_setxattr). >> >> Russ >> >> On Tue, Sep 10, 2013 at 10:22 PM, Gu Zheng wrote: >>> >>> Hi Jaegeuk, >>> On 09/10/2013 08:59 AM, Jaegeuk Kim wrote: >>> Hi, 2013-09-07 (토), 08:00 +, Chao Yu: > Hi Knize, > > Thanks for your reply, I think it's actually meaningless that it's > being named after "spin_lock", > it's better to rename this spinlock to "round_robin_lock". > > This patch can only resolve the issue of unbalanced fs_lock usage, > it can not fix the deadlock issue. > can we fix deadlock issue through this method: > > - vfs_create() > - f2fs_create() - takes an fs_lock and save current thread info into > thread_info[NR_GLOBAL_LOCKS] >- f2fs_add_link() > - __f2fs_add_link() > - init_inode_metadata() > - f2fs_init_security() >- security_inode_init_security() > - f2fs_initxattrs() > - f2fs_setxattr() - get fs_lock only if there is no current > thread info in thread_info > > So it keeps one thread can only hold one fs_lock to avoid deadlock. > Can we use this solution? It could be. But, I think we can avoid to grab the fs_lock at the f2fs_initxattrs() >>> >>> Agree. This fs_lock here is used to protect the xattr from parallel >>> modification, >>> but here is in the initxattrs routine, parallel modification can not >>> happen. >>> And in the normal setxattr routine the inode->i_mutex (vfs layer) is used >>> to >>> avoid parallel modification. So I think this fs_lock is needless. >>> Am I missing something? >>> >>> Regards, >>> Gu >>> level, since this case only happens when f2fs_initxattrs() is called. Let's think about ut in more detail. Thanks, > > > > thanks again! > > > > --- Original Message --- > > Sender : Russ Knize > > Date : 九月 07, 2013 04:25 (GMT+09:00) > > Title : Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better > performance > > > > I encountered this same issue recently and solved it in much the same > way. Can we rename "spin_lock" to something more meaningful? > > > This race actually exposed a potential deadlock between f2fs_create() > and f2fs_initxattrs(): > > > - vfs_create() > - f2fs_create() - takes an fs_lock >- f2fs_add_link() > - __f2fs_add_link() > - init_inode_metadata() > - f2fs_init_security() >- security_inode_init_security() > - f2fs_initxattrs() > - f2fs_setxattr() - also takes an fs_lock > > > If another CPU happens to have the same lock that f2fs_setxattr() was > trying to take because of the race around next_lock_num, we can get > into a deadlock situation if the two threads are also contending over > another resource (like bdi). > > > Another scenario is if the above happens while another thread is in > the middle of grabbing all of the locks via mutex_lock_all(). > f2fs_create() is holding a lock that mutex_lock_all() is waiting for > and mutex_lock_all() is holding a lock that f2fs_setxattr() is waiting > for. > > > Russ > > > On Fri, Sep 6, 2013 at 4:48 AM, Chao Yu wrote: > Hi Kim: > > I think there is a performance problem: when all > sbi->fs_lock is holded, > > then all other threads may get the same next_lock value from > sbi->next_lock_num in function mutex_lock_op, > > and wait to get the same lock at position fs_lock[next_lock], > it unbalance the fs_lock usage. > > It may lost performance when we do the multithread test. > > > >
Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Hi Kim
> -Original Message-
> From: Kim Jaegeuk [mailto:jaegeuk@gmail.com]
> Sent: Wednesday, September 11, 2013 9:15 PM
> To: chao2...@samsung.com
> Cc: ???; 谭姝; linux-fsde...@vger.kernel.org;
linux-ker...@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net
> Subject: Re: Re: [f2fs-dev][PATCH] f2fs: optimize fs_lock for better
performance
>
> Hi,
>
> 2013/9/11 Chao Yu
> >
> > Hi Kim,
> >
> > I did some tests as you mention of using random instead of spin_lock.
> > The test model is as following:
> > eight threads race to grab one of eight locks for one thousand times,
> > and I used four methods to generate lock num:
> >
> > 1.atomic_add_return(1, &sbi->next_lock_num) % NR_GLOBAL_LOCKS;
> > 2.spin_lock(); next_lock_num++ % NR_GLOBAL_LOCKS; spin_unlock();
> > 3.ktime_get().tv64 % NR_GLOBAL_LOCKS;
> > 4.get_random_bytes(&next_lock, sizeof(unsigned int));
> >
> > the result indicate that:
> > max count of collide continuously: 4 > 3 > 2 = 1 max-min count of lock
> > is grabbed: 4 > 3 > 2 = 1 elapsed time of generating: 3 > 2 > 4 > 1
> >
> > So I think it's better to use atomic_add_return in round-robin method
> > to cost less time and reduce collide.
> > What's your opinion?
>
> Could you test with sbi->next_lock_num++ only instead of using
> atomic_add_return?
> IMO, this is just an integer value and still I don't think this value
should be
> covered by any kind of locks.
> Thanks,
Thanks for the advice, I have tested sbi->next_lock_num++.
The time cost of it is a little bit lower than the atomic one's.
for running 8 thread for 100 times test.
the performance of it's balance and collide play quit well than I expected.
Can we modify this patch as following?
root@virtaulmachine:/home/yuchao/git/linux-next/fs/f2fs# git diff --stat
fs/f2fs/f2fs.h |4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
root@virtaulmachine:/home/yuchao/git/linux-next/fs/f2fs# git diff
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 608f0df..7fd99d8 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -544,15 +544,15 @@ static inline void mutex_unlock_all(struct
f2fs_sb_info *sbi)
static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
{
- unsigned char next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
+ unsigned char next_lock;
int i = 0;
for (; i < NR_GLOBAL_LOCKS; i++)
if (mutex_trylock(&sbi->fs_lock[i]))
return i;
+ next_lock = sbi->next_lock_num++ % NR_GLOBAL_LOCKS;
mutex_lock(&sbi->fs_lock[next_lock]);
- sbi->next_lock_num++;
return next_lock;
}
>
> >
> > thanks
> >
> > --- Original Message ---
> > Sender : ??? S5(??)/??/?(???)/
> > Date : 九月 10, 2013 09:52 (GMT+09:00)
> > Title : Re: [f2fs-dev][PATCH] f2fs: optimize fs_lock for better
> > performance
> >
> > Hi,
> >
> > At first, thank you for the report and please follow the email writing
> > rules. :)
> >
> > Anyway, I agree to the below issue.
> > One thing that I can think of is that we don't need to use the
> > spin_lock, since we don't care about the exact lock number, but just
> > need to get any not-collided number.
> >
> > So, how about removing the spin_lock?
> > And how about using a random number?
> > Thanks,
> >
> > 2013-09-06 (?), 09:48 +, Chao Yu:
> > > Hi Kim:
> > >
> > > I think there is a performance problem: when all sbi->fs_lock
> > > is holded,
> > >
> > > then all other threads may get the same next_lock value from
> > > sbi->next_lock_num in function mutex_lock_op,
> > >
> > > and wait to get the same lock at position fs_lock[next_lock], it
> > > unbalance the fs_lock usage.
> > >
> > > It may lost performance when we do the multithread test.
> > >
> > >
> > >
> > > Here is the patch to fix this problem:
> > >
> > >
> > >
> > > Signed-off-by: Yu Chao
> > >
> > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > >
> > > old mode 100644
> > >
> > > new mode 100755
> > >
> > > index 467d42d..983bb45
> > >
> > > --- a/fs/f2fs/f2fs.h
> > >
> > > +++ b/fs/f2fs/f2fs.h
> > >
> > > @@ -371,6 +371,7 @@ struct f2fs_sb_info {
> > >
> > > struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
> > > operations */
> > >
> > > struct mutex node_write;/* locking node
> writes
> > > */
> > >
> > > struct mutex writepages;/* mutex for
> > > writepages() */
> > >
> > > + spinlock_t spin_lock; /* lock for
> > > next_lock_num */
> > >
> > > unsigned char next_lock_num;/* round-robin
> global
> > > locks */
> > >
> > > int por_doing; /* recovery is
> doing
> > > or not */
> > >
> > > int on_build_free_nids; /* build_free_nids is
> > > doing */
> > >
> > > @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
> > > f2fs_sb_info *sbi)
> > >
> > >
> > >
> > > static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
> > >
> > > {
> > >
>
Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Hi Gu
> -Original Message-
> From: Gu Zheng [mailto:guz.f...@cn.fujitsu.com]
> Sent: Wednesday, September 11, 2013 1:38 PM
> To: jaegeuk@samsung.com
> Cc: chao2...@samsung.com; shu@samsung.com;
> linux-fsde...@vger.kernel.org; linux-ker...@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net
> Subject: Re: [f2fs-dev][PATCH] f2fs: optimize fs_lock for better performance
>
> Hi Jaegeuk, Chao,
>
> On 09/10/2013 08:52 AM, Jaegeuk Kim wrote:
>
> > Hi,
> >
> > At first, thank you for the report and please follow the email writing
> > rules. :)
> >
> > Anyway, I agree to the below issue.
> > One thing that I can think of is that we don't need to use the
> > spin_lock, since we don't care about the exact lock number, but just
> > need to get any not-collided number.
>
> IMHO, just moving sbi->next_lock_num++ before
> mutex_lock(&sbi->fs_lock[next_lock])
> can avoid unbalance issue mostly.
> IMO, the case two or more threads increase sbi->next_lock_num in the same
> time is really very very little. If you think it is not rigorous, change
> next_lock_num to atomic one can fix it.
> What's your opinion?
>
> Regards,
> Gu
I did the test sbi->next_lock_num++ compare with the atomic one,
And I found performance of them is almost the same under a small number thread
racing.
So as your and Kim's opinion, it's enough to use "sbi->next_lock_num++" to fix
this issue.
Thanks for the advice.
>
> >
> > So, how about removing the spin_lock?
> > And how about using a random number?
>
> > Thanks,
> >
> > 2013-09-06 (금), 09:48 +, Chao Yu:
> >> Hi Kim:
> >>
> >> I think there is a performance problem: when all sbi->fs_lock is
> >> holded,
> >>
> >> then all other threads may get the same next_lock value from
> >> sbi->next_lock_num in function mutex_lock_op,
> >>
> >> and wait to get the same lock at position fs_lock[next_lock], it
> >> unbalance the fs_lock usage.
> >>
> >> It may lost performance when we do the multithread test.
> >>
> >>
> >>
> >> Here is the patch to fix this problem:
> >>
> >>
> >>
> >> Signed-off-by: Yu Chao
> >>
> >> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>
> >> old mode 100644
> >>
> >> new mode 100755
> >>
> >> index 467d42d..983bb45
> >>
> >> --- a/fs/f2fs/f2fs.h
> >>
> >> +++ b/fs/f2fs/f2fs.h
> >>
> >> @@ -371,6 +371,7 @@ struct f2fs_sb_info {
> >>
> >> struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
> >> operations */
> >>
> >> struct mutex node_write;/* locking node
> writes
> >> */
> >>
> >> struct mutex writepages;/* mutex for
> >> writepages() */
> >>
> >> + spinlock_t spin_lock; /* lock for
> >> next_lock_num */
> >>
> >> unsigned char next_lock_num;/* round-robin
> global
> >> locks */
> >>
> >> int por_doing; /* recovery is doing
> >> or not */
> >>
> >> int on_build_free_nids; /* build_free_nids is
> >> doing */
> >>
> >> @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
> >> f2fs_sb_info *sbi)
> >>
> >>
> >>
> >> static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
> >>
> >> {
> >>
> >> - unsigned char next_lock = sbi->next_lock_num %
> >> NR_GLOBAL_LOCKS;
> >>
> >> + unsigned char next_lock;
> >>
> >> int i = 0;
> >>
> >>
> >>
> >> for (; i < NR_GLOBAL_LOCKS; i++)
> >>
> >> if (mutex_trylock(&sbi->fs_lock[i]))
> >>
> >> return i;
> >>
> >>
> >>
> >> - mutex_lock(&sbi->fs_lock[next_lock]);
> >>
> >> + spin_lock(&sbi->spin_lock);
> >>
> >> + next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
> >>
> >> sbi->next_lock_num++;
> >>
> >> + spin_unlock(&sbi->spin_lock);
> >>
> >> +
> >>
> >> + mutex_lock(&sbi->fs_lock[next_lock]);
> >>
> >> return next_lock;
> >>
> >> }
> >>
> >>
> >>
> >> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >>
> >> old mode 100644
> >>
> >> new mode 100755
> >>
> >> index 75c7dc3..4f27596
> >>
> >> --- a/fs/f2fs/super.c
> >>
> >> +++ b/fs/f2fs/super.c
> >>
> >> @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block
> >> *sb, void *data, int silent)
> >>
> >> mutex_init(&sbi->cp_mutex);
> >>
> >> for (i = 0; i < NR_GLOBAL_LOCKS; i++)
> >>
> >> mutex_init(&sbi->fs_lock[i]);
> >>
> >> + spin_lock_init(&sbi->spin_lock);
> >>
> >> mutex_init(&sbi->node_write);
> >>
> >> sbi->por_doing = 0;
> >>
> >> spin_lock_init(&sbi->stat_lock);
> >>
> >> (END)
> >>
> >>
> >>
> >>
> >>
> >>
> >
>
>
> =
--
How ServiceNow helps IT people transform IT departments:
1. Consolidate legacy IT systems to a single system of record for IT
2. Standardize and globalize service processes across IT
3. Implement zero-touch automation to replace manual, redundant tasks
http://pubads.g.doubleclick.net/gampad/clk
Re: [f2fs-dev] [PATCH] f2fs: optimize fs_lock for better performance
Hi Chao,
On 09/12/2013 10:40 AM, 俞超 wrote:
> Hi Gu
>
>> -Original Message-
>> From: Gu Zheng [mailto:guz.f...@cn.fujitsu.com]
>> Sent: Wednesday, September 11, 2013 1:38 PM
>> To: jaegeuk@samsung.com
>> Cc: chao2...@samsung.com; shu@samsung.com;
>> linux-fsde...@vger.kernel.org; linux-ker...@vger.kernel.org;
>> linux-f2fs-devel@lists.sourceforge.net
>> Subject: Re: [f2fs-dev][PATCH] f2fs: optimize fs_lock for better performance
>>
>> Hi Jaegeuk, Chao,
>>
>> On 09/10/2013 08:52 AM, Jaegeuk Kim wrote:
>>
>>> Hi,
>>>
>>> At first, thank you for the report and please follow the email writing
>>> rules. :)
>>>
>>> Anyway, I agree to the below issue.
>>> One thing that I can think of is that we don't need to use the
>>> spin_lock, since we don't care about the exact lock number, but just
>>> need to get any not-collided number.
>>
>> IMHO, just moving sbi->next_lock_num++ before
>> mutex_lock(&sbi->fs_lock[next_lock])
>> can avoid unbalance issue mostly.
>> IMO, the case two or more threads increase sbi->next_lock_num in the same
>> time is really very very little. If you think it is not rigorous, change
>> next_lock_num to atomic one can fix it.
>> What's your opinion?
>>
>> Regards,
>> Gu
>
> I did the test sbi->next_lock_num++ compare with the atomic one,
> And I found performance of them is almost the same under a small number
> thread racing.
> So as your and Kim's opinion, it's enough to use "sbi->next_lock_num++" to
> fix this issue.
Good, but it seems that your replay patch is out of format, and it's hard for
Jaegeuk to merge.
I'll format it, see the following thread.
Thanks,
Gu
>
> Thanks for the advice.
>>
>>>
>>> So, how about removing the spin_lock?
>>> And how about using a random number?
>>
>>> Thanks,
>>>
>>> 2013-09-06 (금), 09:48 +, Chao Yu:
Hi Kim:
I think there is a performance problem: when all sbi->fs_lock is
holded,
then all other threads may get the same next_lock value from
sbi->next_lock_num in function mutex_lock_op,
and wait to get the same lock at position fs_lock[next_lock], it
unbalance the fs_lock usage.
It may lost performance when we do the multithread test.
Here is the patch to fix this problem:
Signed-off-by: Yu Chao
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
old mode 100644
new mode 100755
index 467d42d..983bb45
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -371,6 +371,7 @@ struct f2fs_sb_info {
struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
operations */
struct mutex node_write;/* locking node
>> writes
*/
struct mutex writepages;/* mutex for
writepages() */
+ spinlock_t spin_lock; /* lock for
next_lock_num */
unsigned char next_lock_num;/* round-robin
>> global
locks */
int por_doing; /* recovery is doing
or not */
int on_build_free_nids; /* build_free_nids is
doing */
@@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
f2fs_sb_info *sbi)
static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
{
- unsigned char next_lock = sbi->next_lock_num %
NR_GLOBAL_LOCKS;
+ unsigned char next_lock;
int i = 0;
for (; i < NR_GLOBAL_LOCKS; i++)
if (mutex_trylock(&sbi->fs_lock[i]))
return i;
- mutex_lock(&sbi->fs_lock[next_lock]);
+ spin_lock(&sbi->spin_lock);
+ next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
sbi->next_lock_num++;
+ spin_unlock(&sbi->spin_lock);
+
+ mutex_lock(&sbi->fs_lock[next_lock]);
return next_lock;
}
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
old mode 100644
new mode 100755
index 75c7dc3..4f27596
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block
*sb, void *data, int silent)
mutex_init(&sbi->cp_mutex);
for (i = 0; i < NR_GLOBAL_LOCKS; i++)
mutex_init(&sbi->fs_lock[i]);
+ spin_lock_init(&sbi->spin_lock);
mutex_init(&sbi->node_write);
sbi->por_doing = 0;
spin_lock_init(&sbi->stat_lock);
(END)
>>>
>>
>>
>> =
>
>
--
How ServiceNow helps IT people transform IT depar
[f2fs-dev] [PATCH V2] f2fs: optimize fs_lock for better performance
From: Yu Chao
There is a performance problem: when all sbi->fs_lock are holded, then
all the following threads may get the same next_lock value from
sbi->next_lock_num
in function mutex_lock_op, and wait for the same lock(fs_lock[next_lock]),
it may cause performance reduce.
So we move the sbi->next_lock_num++ before getting lock, this will average the
following threads if all sbi->fs_lock are holded.
v1-->v2:
Drop the needless spin_lock as Jaegeuk suggested.
Suggested-by: Jaegeuk Kim
Signed-off-by: Yu Chao
Signed-off-by: Gu Zheng
---
fs/f2fs/f2fs.h |4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 608f0df..7fd99d8 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -544,15 +544,15 @@ static inline void mutex_unlock_all(struct f2fs_sb_info
*sbi)
static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
{
- unsigned char next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
+ unsigned char next_lock;
int i = 0;
for (; i < NR_GLOBAL_LOCKS; i++)
if (mutex_trylock(&sbi->fs_lock[i]))
return i;
+ next_lock = sbi->next_lock_num++ % NR_GLOBAL_LOCKS;
mutex_lock(&sbi->fs_lock[next_lock]);
- sbi->next_lock_num++;
return next_lock;
}
--
1.7.7
--
How ServiceNow helps IT people transform IT departments:
1. Consolidate legacy IT systems to a single system of record for IT
2. Standardize and globalize service processes across IT
3. Implement zero-touch automation to replace manual, redundant tasks
http://pubads.g.doubleclick.net/gampad/clk?id=5127&iu=/4140/ostg.clktrk
___
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
