On Fri, Jun 24, 2022 at 01:58:25PM +0800, Jiachen Zhang wrote: > Some users may want both the high performance of the writeback_cahe mode and > a little bit more consistency among FUSE mounts. In the current writeback > mode implementation, users of one FUSE mount can never see the file > expansion done by other FUSE mounts. > > Based on the suggested writeback V2 patch in the upstream mailing-list [1], > this commit allows the cmtime and size to be updated from server in > writeback mode. Compared with the writeback V2 patch in [1], this commit has > several differences: > > 1. Ensure c/mtime are not updated from kernel to server. IOW, the cmtime > generated by kernel are just temporary values that are never flushed to > server, and they can also be updated by the official server cmtime when > the writeback cache is clean. > > 2. Skip mtime-based revalidation when fc->auto_inval_data is set with > fc->writeback_cache_v2. Because the kernel-generated temporary cmtime > are likely not equal to the offical server cmtime. We have a init flag to negotiate FUSE_AUTO_INVAL_DATA to enable/disable fc->auto_inval_data. So should it be filesystem's (user space) responsibility to not use FUSE_AUTO_INVAL_DATA when using FUSE_WRITEBACK_CACHE. I mean, otherwise it is confusing. On one hand filesystem is using FUSE_AUTO_INVAL_DATA but it silently is ingored by kernel because FUSE_WRITEBACK_CACHE is being used as well. will it make more sense to just document it and let filesystem authors enable options carefully. BTW, this probably should be a separate patch in the patch series anyway with proper explanation. Thanks Vivek > > 3. If any page is ever flushed to the server during FUSE_GETATTR > handling on fuse server, even if the cache is clean when > fuse_change_attributes() checks, we should not update the i_size. This > is because the FUSE_GETATTR may get a staled size before the FUSE_WRITE > request changes server inode size. This commit ensures this by > increasing attr_version after writeback for writeback_cache_v2. In that > case, we should also ensure the ordering of the attr_version updating > and the fi->writepages RB-tree updating. So that if a fuse page > writeback ever happens during fuse_change_attributes(), either the > fi->writepages is not empty, or the attr_version is increased. So we > never mistakenly update a stale file size from server to kernel. > > With this patch, writeback mode can consider the server c/mtime as the > official one. When inode attr is timeout or invalidated, kernel has chance > to see size and c/mtime modified by others. > > Together with another patch [2], a FUSE daemon is able to implement > close-to-open (CTO) consistency like what is done in NFS clients. > > [1] https://lore.kernel.org/linux-fsdevel/Ymfu8fGbfYi4FxQ4@xxxxxxxxxxxxxxxxxxxxxxxxx > [2] https://lore.kernel.org/linux-fsdevel/20220608104202.19461-1-zhangjiachen.jaycee@xxxxxxxxxxxxx/ > > Suggested-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> > Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@xxxxxxxxxxxxx> > --- > fs/fuse/file.c | 17 +++++++++++++++ > fs/fuse/fuse_i.h | 3 +++ > fs/fuse/inode.c | 44 +++++++++++++++++++++++++++++++++++++-- > include/uapi/linux/fuse.h | 5 +++++ > 4 files changed, 67 insertions(+), 2 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 9b64e2ff1c96..35bdc7af8468 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -1829,6 +1829,15 @@ static void fuse_writepage_end(struct fuse_mount *fm, struct fuse_args *args, > */ > fuse_send_writepage(fm, next, inarg->offset + inarg->size); > } > + > + if (fc->writeback_cache_v2) > + fi->attr_version = atomic64_inc_return(&fc->attr_version); > + /* > + * Ensure attr_version increases before the page is move out of the > + * writepages rb-tree. > + */ > + smp_mb(); > + > fi->writectr--; > fuse_writepage_finish(fm, wpa); > spin_unlock(&fi->lock); > @@ -1858,10 +1867,18 @@ static struct fuse_file *fuse_write_file_get(struct fuse_inode *fi) > > int fuse_write_inode(struct inode *inode, struct writeback_control *wbc) > { > + struct fuse_conn *fc = get_fuse_conn(inode); > struct fuse_inode *fi = get_fuse_inode(inode); > struct fuse_file *ff; > int err; > > + /* > + * Kernel c/mtime should not be updated to the server in the > + * writeback_cache_v2 mode as server c/mtime are official. > + */ > + if (fc->writeback_cache_v2) > + return 0; > + > /* > * Inode is always written before the last reference is dropped and > * hence this should not be reached from reclaim. > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index 488b460e046f..47de36146fb8 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -654,6 +654,9 @@ struct fuse_conn { > /* show legacy mount options */ > unsigned int legacy_opts_show:1; > > + /* Improved writeback cache policy */ > + unsigned writeback_cache_v2:1; > + > /* > * fs kills suid/sgid/cap on write/chown/trunc. suid is killed on > * write/trunc only if caller did not have CAP_FSETID. sgid is killed > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c > index 8c0665c5dff8..2d5fa82b08b6 100644 > --- a/fs/fuse/inode.c > +++ b/fs/fuse/inode.c > @@ -237,14 +237,41 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr, > u32 cache_mask; > loff_t oldsize; > struct timespec64 old_mtime; > + bool try_wb_update = false; > + > + if (fc->writeback_cache_v2 && S_ISREG(inode->i_mode)) { > + inode_lock(inode); > + try_wb_update = true; > + } > > spin_lock(&fi->lock); > /* > * In case of writeback_cache enabled, writes update mtime, ctime and > * may update i_size. In these cases trust the cached value in the > * inode. > + * > + * In writeback_cache_v2 mode, if all the following conditions are met, > + * then we allow the attributes to be refreshed: > + * > + * - inode is not in the process of being written (I_SYNC) > + * - inode has no dirty pages (I_DIRTY_PAGES) > + * - inode data-related attributes are clean (I_DIRTY_DATASYNC) > + * - inode does not have any page writeback in progress > + * > + * Note: checking PAGECACHE_TAG_WRITEBACK is not sufficient in fuse, > + * since inode can appear to have no PageWriteback pages, yet still have > + * outstanding write request. > */ > cache_mask = fuse_get_cache_mask(inode); > + if (try_wb_update && !(inode->i_state & (I_DIRTY_PAGES | I_SYNC | > + I_DIRTY_DATASYNC)) && RB_EMPTY_ROOT(&fi->writepages)) > + cache_mask &= ~(STATX_MTIME | STATX_CTIME | STATX_SIZE); > + /* > + * Ensure the ordering of cleanness checking and following attr_version > + * comparison. > + */ > + smp_mb(); > + > if (cache_mask & STATX_SIZE) > attr->size = i_size_read(inode); > > @@ -283,7 +310,13 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr, > truncate_pagecache(inode, attr->size); > if (!fc->explicit_inval_data) > inval = true; > - } else if (fc->auto_inval_data) { > + } else if (!fc->writeback_cache_v2 && fc->auto_inval_data) { > + /* > + * When fc->writeback_cache_v2 is set, the old_mtime > + * can be generated by kernel and must not equal to > + * new_mtime generated by server. So skip in such > + * case. > + */ > struct timespec64 new_mtime = { > .tv_sec = attr->mtime, > .tv_nsec = attr->mtimensec, > @@ -303,6 +336,9 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr, > > if (IS_ENABLED(CONFIG_FUSE_DAX)) > fuse_dax_dontcache(inode, attr->flags); > + > + if (try_wb_update) > + inode_unlock(inode); > } > > static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr) > @@ -1153,6 +1189,10 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args, > fc->async_dio = 1; > if (flags & FUSE_WRITEBACK_CACHE) > fc->writeback_cache = 1; > + if (flags & FUSE_WRITEBACK_CACHE_V2) { > + fc->writeback_cache = 1; > + fc->writeback_cache_v2 = 1; > + } > if (flags & FUSE_PARALLEL_DIROPS) > fc->parallel_dirops = 1; > if (flags & FUSE_HANDLE_KILLPRIV) > @@ -1234,7 +1274,7 @@ void fuse_send_init(struct fuse_mount *fm) > FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS | > FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA | > FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT | FUSE_INIT_EXT | > - FUSE_SECURITY_CTX; > + FUSE_SECURITY_CTX | FUSE_WRITEBACK_CACHE_V2; > #ifdef CONFIG_FUSE_DAX > if (fm->fc->dax) > flags |= FUSE_MAP_ALIGNMENT; > diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h > index d6ccee961891..b474763bcf59 100644 > --- a/include/uapi/linux/fuse.h > +++ b/include/uapi/linux/fuse.h > @@ -194,6 +194,7 @@ > * - add FUSE_SECURITY_CTX init flag > * - add security context to create, mkdir, symlink, and mknod requests > * - add FUSE_HAS_INODE_DAX, FUSE_ATTR_DAX > + * - add FUSE_WRITEBACK_CACHE_V2 init flag > */ > > #ifndef _LINUX_FUSE_H > @@ -353,6 +354,9 @@ struct fuse_file_lock { > * FUSE_SECURITY_CTX: add security context to create, mkdir, symlink, and > * mknod > * FUSE_HAS_INODE_DAX: use per inode DAX > + * FUSE_WRITEBACK_CACHE_V2: > + * allow time/size to be refreshed if no pending write > + * c/mtime not updated from kernel to server > */ > #define FUSE_ASYNC_READ (1 << 0) > #define FUSE_POSIX_LOCKS (1 << 1) > @@ -389,6 +393,7 @@ struct fuse_file_lock { > /* bits 32..63 get shifted down 32 bits into the flags2 field */ > #define FUSE_SECURITY_CTX (1ULL << 32) > #define FUSE_HAS_INODE_DAX (1ULL << 33) > +#define FUSE_WRITEBACK_CACHE_V2 (1ULL << 34) > > /** > * CUSE INIT request/reply flags > -- > 2.20.1 >
