| Message ID | 20200925120655.295142-27-dgilbert@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [PULL,01/26] migration: Properly destroy variables on incoming side | expand |
On Fri, Sep 25, 2020 at 01:06:55PM +0100, Dr. David Alan Gilbert (git) wrote: > From: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com> > > Due to the commit 65da4539803373ec4eec97ffc49ee90083e56efd, the O_DIRECT > open flag of guest applications will be discarded by virtiofsd. While > this behavior makes it consistent with the virtio-9p scheme when guest > applications use direct I/O, we no longer have any chance to bypass the > host page cache. > > Therefore, we add a flag 'allow_direct_io' to lo_data. If '-o > no_allow_direct_io' option is added, or none of '-o allow_direct_io' or > '-o no_allow_direct_io' is added, the 'allow_direct_io' will be set to > 0, and virtiofsd discards O_DIRECT as before. If '-o allow_direct_io' > is added to the starting command-line, 'allow_direct_io' will be set to > 1, so that the O_DIRECT flags will be retained and host page cache can > be bypassed. Hi Jiachen, Curious that in what cases you want to bypass host page cache. Thanks Vivek > > Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> > Message-Id: <20200824105957.61265-1-zhangjiachen.jaycee@bytedance.com> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > --- > tools/virtiofsd/helper.c | 4 ++++ > tools/virtiofsd/passthrough_ll.c | 20 ++++++++++++++------ > 2 files changed, 18 insertions(+), 6 deletions(-) > > diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c > index 7bc5d7dc5a..85770d63f1 100644 > --- a/tools/virtiofsd/helper.c > +++ b/tools/virtiofsd/helper.c > @@ -178,6 +178,10 @@ void fuse_cmdline_help(void) > " (0 leaves rlimit unchanged)\n" > " default: min(1000000, fs.file-max - 16384)\n" > " if the current rlimit is lower\n" > + " -o allow_direct_io|no_allow_direct_io\n" > + " retain/discard O_DIRECT flags passed down\n" > + " to virtiofsd from guest applications.\n" > + " default: no_allow_direct_io\n" > ); > } > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index 784330e0e4..0b229ebd57 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -151,6 +151,7 @@ struct lo_data { > int timeout_set; > int readdirplus_set; > int readdirplus_clear; > + int allow_direct_io; > struct lo_inode root; > GHashTable *inodes; /* protected by lo->mutex */ > struct lo_map ino_map; /* protected by lo->mutex */ > @@ -179,6 +180,8 @@ static const struct fuse_opt lo_opts[] = { > { "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS }, > { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 }, > { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 }, > + { "allow_direct_io", offsetof(struct lo_data, allow_direct_io), 1 }, > + { "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), 0 }, > FUSE_OPT_END > }; > static bool use_syslog = false; > @@ -1516,7 +1519,8 @@ static void lo_releasedir(fuse_req_t req, fuse_ino_t ino, > fuse_reply_err(req, 0); > } > > -static void update_open_flags(int writeback, struct fuse_file_info *fi) > +static void update_open_flags(int writeback, int allow_direct_io, > + struct fuse_file_info *fi) > { > /* > * With writeback cache, kernel may send read requests even > @@ -1541,10 +1545,13 @@ static void update_open_flags(int writeback, struct fuse_file_info *fi) > > /* > * O_DIRECT in guest should not necessarily mean bypassing page > - * cache on host as well. If somebody needs that behavior, it > - * probably should be a configuration knob in daemon. > + * cache on host as well. Therefore, we discard it by default > + * ('-o no_allow_direct_io'). If somebody needs that behavior, > + * the '-o allow_direct_io' option should be set. > */ > - fi->flags &= ~O_DIRECT; > + if (!allow_direct_io) { > + fi->flags &= ~O_DIRECT; > + } > } > > static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, > @@ -1576,7 +1583,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, > goto out; > } > > - update_open_flags(lo->writeback, fi); > + update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW, > mode); > @@ -1786,7 +1793,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi) > fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino, > fi->flags); > > - update_open_flags(lo->writeback, fi); > + update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > sprintf(buf, "%i", lo_fd(req, ino)); > fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); > @@ -2823,6 +2830,7 @@ int main(int argc, char *argv[]) > .debug = 0, > .writeback = 0, > .posix_lock = 0, > + .allow_direct_io = 0, > .proc_self_fd = -1, > }; > struct lo_map_elem *root_elem; > -- > 2.26.2 >
On Wed, Sep 30, 2020 at 5:53 AM Vivek Goyal <vgoyal@redhat.com> wrote: > On Fri, Sep 25, 2020 at 01:06:55PM +0100, Dr. David Alan Gilbert (git) > wrote: > > From: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com> > > > > Due to the commit 65da4539803373ec4eec97ffc49ee90083e56efd, the O_DIRECT > > open flag of guest applications will be discarded by virtiofsd. While > > this behavior makes it consistent with the virtio-9p scheme when guest > > applications use direct I/O, we no longer have any chance to bypass the > > host page cache. > > > > Therefore, we add a flag 'allow_direct_io' to lo_data. If '-o > > no_allow_direct_io' option is added, or none of '-o allow_direct_io' or > > '-o no_allow_direct_io' is added, the 'allow_direct_io' will be set to > > 0, and virtiofsd discards O_DIRECT as before. If '-o allow_direct_io' > > is added to the starting command-line, 'allow_direct_io' will be set to > > 1, so that the O_DIRECT flags will be retained and host page cache can > > be bypassed. > > Hi Jiachen, > > Curious that in what cases you want to bypass host page cache. > > Thanks > Vivek > Hi Vivek, Some apps like DBMS may allocate their own file cache in userspace, so they may want to bypass kernel page cache by using O_DIRECT. When these apps are running in guest and access virtio-fs files, we'd better obey these needs. This can also eliminate the host memory usage. Another case is when we perform file I/O benchmarks on different storage devices (like HDD and SSD), it's not that fair to introduce ram caches. By using "cache=none" with "allow_direct_io", we can bypass guest and host page caches, and access the storage devices directly. Best wishes, Jiachen > > > > Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com> > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> > > Message-Id: <20200824105957.61265-1-zhangjiachen.jaycee@bytedance.com> > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > > --- > > tools/virtiofsd/helper.c | 4 ++++ > > tools/virtiofsd/passthrough_ll.c | 20 ++++++++++++++------ > > 2 files changed, 18 insertions(+), 6 deletions(-) > > > > diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c > > index 7bc5d7dc5a..85770d63f1 100644 > > --- a/tools/virtiofsd/helper.c > > +++ b/tools/virtiofsd/helper.c > > @@ -178,6 +178,10 @@ void fuse_cmdline_help(void) > > " (0 leaves rlimit > unchanged)\n" > > " default: min(1000000, > fs.file-max - 16384)\n" > > " if the current > rlimit is lower\n" > > + " -o allow_direct_io|no_allow_direct_io\n" > > + " retain/discard O_DIRECT > flags passed down\n" > > + " to virtiofsd from guest > applications.\n" > > + " default: > no_allow_direct_io\n" > > ); > > } > > > > diff --git a/tools/virtiofsd/passthrough_ll.c > b/tools/virtiofsd/passthrough_ll.c > > index 784330e0e4..0b229ebd57 100644 > > --- a/tools/virtiofsd/passthrough_ll.c > > +++ b/tools/virtiofsd/passthrough_ll.c > > @@ -151,6 +151,7 @@ struct lo_data { > > int timeout_set; > > int readdirplus_set; > > int readdirplus_clear; > > + int allow_direct_io; > > struct lo_inode root; > > GHashTable *inodes; /* protected by lo->mutex */ > > struct lo_map ino_map; /* protected by lo->mutex */ > > @@ -179,6 +180,8 @@ static const struct fuse_opt lo_opts[] = { > > { "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS }, > > { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 }, > > { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 > }, > > + { "allow_direct_io", offsetof(struct lo_data, allow_direct_io), 1 }, > > + { "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), > 0 }, > > FUSE_OPT_END > > }; > > static bool use_syslog = false; > > @@ -1516,7 +1519,8 @@ static void lo_releasedir(fuse_req_t req, > fuse_ino_t ino, > > fuse_reply_err(req, 0); > > } > > > > -static void update_open_flags(int writeback, struct fuse_file_info *fi) > > +static void update_open_flags(int writeback, int allow_direct_io, > > + struct fuse_file_info *fi) > > { > > /* > > * With writeback cache, kernel may send read requests even > > @@ -1541,10 +1545,13 @@ static void update_open_flags(int writeback, > struct fuse_file_info *fi) > > > > /* > > * O_DIRECT in guest should not necessarily mean bypassing page > > - * cache on host as well. If somebody needs that behavior, it > > - * probably should be a configuration knob in daemon. > > + * cache on host as well. Therefore, we discard it by default > > + * ('-o no_allow_direct_io'). If somebody needs that behavior, > > + * the '-o allow_direct_io' option should be set. > > */ > > - fi->flags &= ~O_DIRECT; > > + if (!allow_direct_io) { > > + fi->flags &= ~O_DIRECT; > > + } > > } > > > > static void lo_create(fuse_req_t req, fuse_ino_t parent, const char > *name, > > @@ -1576,7 +1583,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t > parent, const char *name, > > goto out; > > } > > > > - update_open_flags(lo->writeback, fi); > > + update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > > > fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & > ~O_NOFOLLOW, > > mode); > > @@ -1786,7 +1793,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t > ino, struct fuse_file_info *fi) > > fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", > ino, > > fi->flags); > > > > - update_open_flags(lo->writeback, fi); > > + update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > > > sprintf(buf, "%i", lo_fd(req, ino)); > > fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); > > @@ -2823,6 +2830,7 @@ int main(int argc, char *argv[]) > > .debug = 0, > > .writeback = 0, > > .posix_lock = 0, > > + .allow_direct_io = 0, > > .proc_self_fd = -1, > > }; > > struct lo_map_elem *root_elem; > > -- > > 2.26.2 > > > >
diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c index 7bc5d7dc5a..85770d63f1 100644 --- a/tools/virtiofsd/helper.c +++ b/tools/virtiofsd/helper.c @@ -178,6 +178,10 @@ void fuse_cmdline_help(void) " (0 leaves rlimit unchanged)\n" " default: min(1000000, fs.file-max - 16384)\n" " if the current rlimit is lower\n" + " -o allow_direct_io|no_allow_direct_io\n" + " retain/discard O_DIRECT flags passed down\n" + " to virtiofsd from guest applications.\n" + " default: no_allow_direct_io\n" ); } diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 784330e0e4..0b229ebd57 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -151,6 +151,7 @@ struct lo_data { int timeout_set; int readdirplus_set; int readdirplus_clear; + int allow_direct_io; struct lo_inode root; GHashTable *inodes; /* protected by lo->mutex */ struct lo_map ino_map; /* protected by lo->mutex */ @@ -179,6 +180,8 @@ static const struct fuse_opt lo_opts[] = { { "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS }, { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 }, { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 }, + { "allow_direct_io", offsetof(struct lo_data, allow_direct_io), 1 }, + { "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), 0 }, FUSE_OPT_END }; static bool use_syslog = false; @@ -1516,7 +1519,8 @@ static void lo_releasedir(fuse_req_t req, fuse_ino_t ino, fuse_reply_err(req, 0); } -static void update_open_flags(int writeback, struct fuse_file_info *fi) +static void update_open_flags(int writeback, int allow_direct_io, + struct fuse_file_info *fi) { /* * With writeback cache, kernel may send read requests even @@ -1541,10 +1545,13 @@ static void update_open_flags(int writeback, struct fuse_file_info *fi) /* * O_DIRECT in guest should not necessarily mean bypassing page - * cache on host as well. If somebody needs that behavior, it - * probably should be a configuration knob in daemon. + * cache on host as well. Therefore, we discard it by default + * ('-o no_allow_direct_io'). If somebody needs that behavior, + * the '-o allow_direct_io' option should be set. */ - fi->flags &= ~O_DIRECT; + if (!allow_direct_io) { + fi->flags &= ~O_DIRECT; + } } static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, @@ -1576,7 +1583,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, goto out; } - update_open_flags(lo->writeback, fi); + update_open_flags(lo->writeback, lo->allow_direct_io, fi); fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW, mode); @@ -1786,7 +1793,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi) fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino, fi->flags); - update_open_flags(lo->writeback, fi); + update_open_flags(lo->writeback, lo->allow_direct_io, fi); sprintf(buf, "%i", lo_fd(req, ino)); fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); @@ -2823,6 +2830,7 @@ int main(int argc, char *argv[]) .debug = 0, .writeback = 0, .posix_lock = 0, + .allow_direct_io = 0, .proc_self_fd = -1, }; struct lo_map_elem *root_elem;