Message ID | 20200924055958.825515-1-lihao2018.fnst@cn.fujitsu.com (mailing list archive) |
---|---|
State | Superseded |
Headers | show |
Series | [v2] fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set | expand |
On Thu 24-09-20 13:59:58, Hao Li wrote: > If DCACHE_REFERENCED is set, fast_dput() will return true, and then > retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result, > the dentry won't be killed and the corresponding inode can't be evicted. > In the following example, the DAX policy can't take effects unless we > do a drop_caches manually. > > # DCACHE_LRU_LIST will be set > echo abcdefg > test.txt > > # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything > xfs_io -c 'chattr +x' test.txt > > # Drop caches to make DAX changing take effects > echo 2 > /proc/sys/vm/drop_caches > > What this patch does is preventing fast_dput() from returning true if > DCACHE_DONTCACHE is set. Then retain_dentry() will detect the > DCACHE_DONTCACHE and will return false. As a result, the dentry will be > killed and the inode will be evicted. In this way, if we change per-file > DAX policy, it will take effects automatically after this file is closed > by all processes. > > I also add some comments to make the code more clear. > > Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com> The patch looks good to me. You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > v1 is split into two standalone patch as discussed in [1], and the first > patch has been reviewed in [2]. This is the second patch. > > [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ > [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/ > > fs/dcache.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index ea0485861d93..97e81a844a96 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) > * a reference to the dentry and change that, but > * our work is done - we can leave the dentry > * around with a zero refcount. > + * > + * Nevertheless, there are two cases that we should kill > + * the dentry anyway. > + * 1. free disconnected dentries as soon as their refcount > + * reached zero. > + * 2. free dentries if they should not be cached. > */ > smp_rmb(); > d_flags = READ_ONCE(dentry->d_flags); > - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; > + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | > + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; > > /* Nothing to do? Dropping the reference was all we needed? */ > if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) > -- > 2.28.0 > > >
On Thu, Sep 24, 2020 at 01:59:58PM +0800, Hao Li wrote: > If DCACHE_REFERENCED is set, fast_dput() will return true, and then > retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result, > the dentry won't be killed and the corresponding inode can't be evicted. > In the following example, the DAX policy can't take effects unless we > do a drop_caches manually. > > # DCACHE_LRU_LIST will be set > echo abcdefg > test.txt > > # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything > xfs_io -c 'chattr +x' test.txt > > # Drop caches to make DAX changing take effects > echo 2 > /proc/sys/vm/drop_caches > > What this patch does is preventing fast_dput() from returning true if > DCACHE_DONTCACHE is set. Then retain_dentry() will detect the > DCACHE_DONTCACHE and will return false. As a result, the dentry will be > killed and the inode will be evicted. In this way, if we change per-file > DAX policy, it will take effects automatically after this file is closed > by all processes. > > I also add some comments to make the code more clear. > > Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> > --- > v1 is split into two standalone patch as discussed in [1], and the first > patch has been reviewed in [2]. This is the second patch. > > [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ > [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/ > > fs/dcache.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index ea0485861d93..97e81a844a96 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) > * a reference to the dentry and change that, but > * our work is done - we can leave the dentry > * around with a zero refcount. > + * > + * Nevertheless, there are two cases that we should kill > + * the dentry anyway. > + * 1. free disconnected dentries as soon as their refcount > + * reached zero. > + * 2. free dentries if they should not be cached. > */ > smp_rmb(); > d_flags = READ_ONCE(dentry->d_flags); > - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; > + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | > + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; > > /* Nothing to do? Dropping the reference was all we needed? */ > if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) > -- > 2.28.0 > > >
Hum, Al, did this patch get lost? Honza On Thu 24-09-20 16:58:56, Jan Kara wrote: > On Thu 24-09-20 13:59:58, Hao Li wrote: > > If DCACHE_REFERENCED is set, fast_dput() will return true, and then > > retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result, > > the dentry won't be killed and the corresponding inode can't be evicted. > > In the following example, the DAX policy can't take effects unless we > > do a drop_caches manually. > > > > # DCACHE_LRU_LIST will be set > > echo abcdefg > test.txt > > > > # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything > > xfs_io -c 'chattr +x' test.txt > > > > # Drop caches to make DAX changing take effects > > echo 2 > /proc/sys/vm/drop_caches > > > > What this patch does is preventing fast_dput() from returning true if > > DCACHE_DONTCACHE is set. Then retain_dentry() will detect the > > DCACHE_DONTCACHE and will return false. As a result, the dentry will be > > killed and the inode will be evicted. In this way, if we change per-file > > DAX policy, it will take effects automatically after this file is closed > > by all processes. > > > > I also add some comments to make the code more clear. > > > > Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com> > > The patch looks good to me. You can add: > > Reviewed-by: Jan Kara <jack@suse.cz> > > Honza > > > --- > > v1 is split into two standalone patch as discussed in [1], and the first > > patch has been reviewed in [2]. This is the second patch. > > > > [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ > > [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/ > > > > fs/dcache.c | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/fs/dcache.c b/fs/dcache.c > > index ea0485861d93..97e81a844a96 100644 > > --- a/fs/dcache.c > > +++ b/fs/dcache.c > > @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) > > * a reference to the dentry and change that, but > > * our work is done - we can leave the dentry > > * around with a zero refcount. > > + * > > + * Nevertheless, there are two cases that we should kill > > + * the dentry anyway. > > + * 1. free disconnected dentries as soon as their refcount > > + * reached zero. > > + * 2. free dentries if they should not be cached. > > */ > > smp_rmb(); > > d_flags = READ_ONCE(dentry->d_flags); > > - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; > > + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | > > + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; > > > > /* Nothing to do? Dropping the reference was all we needed? */ > > if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) > > -- > > 2.28.0 > > > > > > > -- > Jan Kara <jack@suse.com> > SUSE Labs, CR
Ping :) On 2020/10/21 21:51, Jan Kara wrote: > Hum, Al, did this patch get lost? > > Honza > > On Thu 24-09-20 16:58:56, Jan Kara wrote: >> On Thu 24-09-20 13:59:58, Hao Li wrote: >>> If DCACHE_REFERENCED is set, fast_dput() will return true, and then >>> retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result, >>> the dentry won't be killed and the corresponding inode can't be evicted. >>> In the following example, the DAX policy can't take effects unless we >>> do a drop_caches manually. >>> >>> # DCACHE_LRU_LIST will be set >>> echo abcdefg > test.txt >>> >>> # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything >>> xfs_io -c 'chattr +x' test.txt >>> >>> # Drop caches to make DAX changing take effects >>> echo 2 > /proc/sys/vm/drop_caches >>> >>> What this patch does is preventing fast_dput() from returning true if >>> DCACHE_DONTCACHE is set. Then retain_dentry() will detect the >>> DCACHE_DONTCACHE and will return false. As a result, the dentry will be >>> killed and the inode will be evicted. In this way, if we change per-file >>> DAX policy, it will take effects automatically after this file is closed >>> by all processes. >>> >>> I also add some comments to make the code more clear. >>> >>> Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com> >> The patch looks good to me. You can add: >> >> Reviewed-by: Jan Kara <jack@suse.cz> >> >> Honza >> >>> --- >>> v1 is split into two standalone patch as discussed in [1], and the first >>> patch has been reviewed in [2]. This is the second patch. >>> >>> [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ >>> [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/ >>> >>> fs/dcache.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/dcache.c b/fs/dcache.c >>> index ea0485861d93..97e81a844a96 100644 >>> --- a/fs/dcache.c >>> +++ b/fs/dcache.c >>> @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) >>> * a reference to the dentry and change that, but >>> * our work is done - we can leave the dentry >>> * around with a zero refcount. >>> + * >>> + * Nevertheless, there are two cases that we should kill >>> + * the dentry anyway. >>> + * 1. free disconnected dentries as soon as their refcount >>> + * reached zero. >>> + * 2. free dentries if they should not be cached. >>> */ >>> smp_rmb(); >>> d_flags = READ_ONCE(dentry->d_flags); >>> - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; >>> + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | >>> + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; >>> >>> /* Nothing to do? Dropping the reference was all we needed? */ >>> if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) >>> -- >>> 2.28.0 >>> >>> >>> >> -- >> Jan Kara <jack@suse.com> >> SUSE Labs, CR
diff --git a/fs/dcache.c b/fs/dcache.c index ea0485861d93..97e81a844a96 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) * a reference to the dentry and change that, but * our work is done - we can leave the dentry * around with a zero refcount. + * + * Nevertheless, there are two cases that we should kill + * the dentry anyway. + * 1. free disconnected dentries as soon as their refcount + * reached zero. + * 2. free dentries if they should not be cached. */ smp_rmb(); d_flags = READ_ONCE(dentry->d_flags); - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; /* Nothing to do? Dropping the reference was all we needed? */ if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
If DCACHE_REFERENCED is set, fast_dput() will return true, and then retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result, the dentry won't be killed and the corresponding inode can't be evicted. In the following example, the DAX policy can't take effects unless we do a drop_caches manually. # DCACHE_LRU_LIST will be set echo abcdefg > test.txt # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything xfs_io -c 'chattr +x' test.txt # Drop caches to make DAX changing take effects echo 2 > /proc/sys/vm/drop_caches What this patch does is preventing fast_dput() from returning true if DCACHE_DONTCACHE is set. Then retain_dentry() will detect the DCACHE_DONTCACHE and will return false. As a result, the dentry will be killed and the inode will be evicted. In this way, if we change per-file DAX policy, it will take effects automatically after this file is closed by all processes. I also add some comments to make the code more clear. Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com> --- v1 is split into two standalone patch as discussed in [1], and the first patch has been reviewed in [2]. This is the second patch. [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/ fs/dcache.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)