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Re: [PULL 26/26] virtiofsd: Add -o allow_direct_io|no_allow_direct_io op
From: |
Vivek Goyal |
Subject: |
Re: [PULL 26/26] virtiofsd: Add -o allow_direct_io|no_allow_direct_io options |
Date: |
Tue, 29 Sep 2020 17:53:19 -0400 |
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
>
- [PULL 16/26] migration: increase max-bandwidth to 128 MiB/s (1 Gib/s), (continued)
- [PULL 16/26] migration: increase max-bandwidth to 128 MiB/s (1 Gib/s), Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 17/26] migration/tls: save hostname into MigrationState, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 18/26] migration/tls: extract migration_tls_client_create for common-use, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 19/26] migration/tls: add tls_hostname into MultiFDSendParams, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 20/26] migration/tls: extract cleanup function for common-use, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 21/26] migration/tls: add support for multifd tls-handshake, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 22/26] migration/tls: add trace points for multifd-tls, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 24/26] virtiofsd: document cache=auto default, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 25/26] virtiofsd: Used glib "shared" thread pool, Dr. David Alan Gilbert (git), 2020/09/25
- [PULL 26/26] virtiofsd: Add -o allow_direct_io|no_allow_direct_io options, Dr. David Alan Gilbert (git), 2020/09/25
- Re: [PULL 26/26] virtiofsd: Add -o allow_direct_io|no_allow_direct_io options,
Vivek Goyal <=
- [PULL 23/26] monitor: Use LOCK_GUARD macros, Dr. David Alan Gilbert (git), 2020/09/25
- Re: [PULL 00/26] migration and friends queue, no-reply, 2020/09/25
- Re: [PULL 00/26] migration and friends queue, Peter Maydell, 2020/09/25