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@xxxxxxxxxxxxxx> >> The patch looks good to me. You can add: >> >> Reviewed-by: Jan Kara <jack@xxxxxxx> >> >> 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@xxxxxxxxxxxxxxxxxxx/ >>> [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@xxxxxxxxxxxxxxxxxxx/ >>> >>> 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@xxxxxxxx> >> SUSE Labs, CR
