Keiichi Watanabe
2023-Jun-20 15:13 UTC
[PATCH 0/3] Support negative dentry cache for FUSE and virtiofs
This patch series adds a new mount option called negative_dentry_timeout for FUSE and virtio-fs filesystems. This option allows the kernel to cache negative dentries, which are dentries that represent a non-existent file. When this option is enabled, the kernel will skip FUSE_LOOKUP requests for second and subsequent lookups to a non-existent file. Unlike negative dentry caches on a normal filesystem such as ext4, the kernel may need to refresh the cache for FUSE and virtio-fs filesystems. This is because the kernel does not know when a FUSE server or a virtio-fs device creates or deletes files. To address this, the new negative_dentry_timeout option takes an expiration time for cache entries. The appropriate timeout duration should be determined by considering how often a FUSE server updates file paths and the amount of memory the kernel can use for the cache. As we evaluated the virtio-fs's performance on a guest Linux on crosvm [1]'s virtiofs device[2], the `negative_dentry_timeout` option saved ~1 second per 10000 `stat` call against a non-existent path. The experiment settings and results are as follows: * Command to start VM with crosvm: sudo crosvm run \ --disable-sandbox \ --cpus 1 \ --mem 2048 \ --rwroot debian.img \ --shared-dir \ /path/:my_virtiofs:type=fs:cache=always:timeout=3600 \ -p "console=hvc0 init=/bin/bash" \ vmlinux * Mount command in the guest Default: $ mount -t virtiofs my_virtiofs ./workspace/ With negative dentry cache: $ mount -t virtiofs -o negative_dentry_timeout=10 my_virtiofs ./workspace/ * Test commands $ cd workspace $ echo 3 > /proc/sys/vm/drop_caches $ time for i in `seq 1 10000`; \ do stat non-existent.txt 2> /dev/null; \ done * Results: Default: real 0m12.606s user 0m3.624s sys 0m7.756s With `-o negative_dentry_timeout=10`: real 0m11.276s user 0m3.514s sys 0m7.544s [1]: https://crosvm.dev/book/ [2]: https://crosvm.dev/book/devices/fs.html Keiichi Watanabe (3): docs: virtiofs: Fix descriptions about virtiofs mount option fuse: Add negative_dentry_timeout option virtiofs: Add negative_dentry_timeout option Documentation/filesystems/dax.rst | 1 + Documentation/filesystems/fuse.rst | 6 ++++++ Documentation/filesystems/virtiofs.rst | 9 ++++++++- fs/fuse/dir.c | 3 ++- fs/fuse/fuse_i.h | 4 ++++ fs/fuse/inode.c | 12 +++++++++++- fs/fuse/virtio_fs.c | 8 ++++++++ 7 files changed, 40 insertions(+), 3 deletions(-) -- 2.41.0.185.g7c58973941-goog
Keiichi Watanabe
2023-Jun-20 15:13 UTC
[PATCH 1/3] docs: virtiofs: Fix descriptions about virtiofs mount option
Since virtiofs and FUSE don't share mount options, fixes the description. Also, explains DAX option as the only virtiofs-specific option so far. Signed-off-by: Keiichi Watanabe <keiichiw at chromium.org> --- Documentation/filesystems/dax.rst | 1 + Documentation/filesystems/virtiofs.rst | 5 ++++- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/Documentation/filesystems/dax.rst b/Documentation/filesystems/dax.rst index c04609d8ee24..77c5d4550ecd 100644 --- a/Documentation/filesystems/dax.rst +++ b/Documentation/filesystems/dax.rst @@ -167,6 +167,7 @@ Setting the `FS_XFLAG_DAX` flag (specifically or through inheritance) occurs eve if the underlying media does not support dax and/or the filesystem is overridden with a mount option. +.. _virtiofs-dax: Enabling DAX on virtiofs ---------------------------- diff --git a/Documentation/filesystems/virtiofs.rst b/Documentation/filesystems/virtiofs.rst index fd4d2484e949..fdec5a7840f7 100644 --- a/Documentation/filesystems/virtiofs.rst +++ b/Documentation/filesystems/virtiofs.rst @@ -43,7 +43,10 @@ Mount options ------------- virtiofs supports general VFS mount options, for example, remount, -ro, rw, context, etc. It also supports FUSE mount options. +ro, rw, context, etc. Also, virtiofs has its own options. + +dax[=always,never,inode] + Enable direct access for files. See :ref:`virtiofs-dax`. atime behavior ^^^^^^^^^^^^^^ -- 2.41.0.185.g7c58973941-goog
Keiichi Watanabe
2023-Jun-20 15:13 UTC
[PATCH 3/3] virtiofs: Add negative_dentry_timeout option
Add negative_dentry_timeout mount option to virtiofs to caching negative
dentry on the guest side. When the host virito-fs device has an exclusive
access to the file system and the machine has enough memory, one can
specify a long time as the timeout.
This option saves ~1 second per 10,000 stat request for non-existing paths.
Signed-off-by: Keiichi Watanabe <keiichiw at chromium.org>
---
Documentation/filesystems/virtiofs.rst | 4 ++++
fs/fuse/virtio_fs.c | 8 ++++++++
2 files changed, 12 insertions(+)
diff --git a/Documentation/filesystems/virtiofs.rst
b/Documentation/filesystems/virtiofs.rst
index fdec5a7840f7..b045ef2223de 100644
--- a/Documentation/filesystems/virtiofs.rst
+++ b/Documentation/filesystems/virtiofs.rst
@@ -48,6 +48,10 @@ ro, rw, context, etc. Also, virtiofs has its own options.
dax[=always,never,inode]
Enable direct access for files. See :ref:`virtiofs-dax`.
+negative_dentry_timeout=N
+ Set the time in seconds to keep negative dentry cache. Same as the FUSE's
+ mount option.
+
atime behavior
^^^^^^^^^^^^^^
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 4d8d4f16c727..bbbd840510f9 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -99,11 +99,13 @@ static const struct constant_table dax_param_enums[] = {
enum {
OPT_DAX,
OPT_DAX_ENUM,
+ OPT_NEGATIVE_DENTRY_TIMEOUT,
};
static const struct fs_parameter_spec virtio_fs_parameters[] = {
fsparam_flag("dax", OPT_DAX),
fsparam_enum("dax", OPT_DAX_ENUM, dax_param_enums),
+ fsparam_u32 ("negative_dentry_timeout",
OPT_NEGATIVE_DENTRY_TIMEOUT),
{}
};
@@ -125,6 +127,9 @@ static int virtio_fs_parse_param(struct fs_context *fsc,
case OPT_DAX_ENUM:
ctx->dax_mode = result.uint_32;
break;
+ case OPT_NEGATIVE_DENTRY_TIMEOUT:
+ ctx->negative_dentry_timeout = result.uint_32;
+ break;
default:
return -EINVAL;
}
@@ -1416,6 +1421,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
struct super_block *sb;
struct fuse_conn *fc = NULL;
struct fuse_mount *fm;
+ struct fuse_fs_context *ffc;
unsigned int virtqueue_size;
int err = -EIO;
@@ -1468,6 +1474,8 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
sb->s_flags |= SB_ACTIVE;
}
+ ffc = fsc->fs_private;
+ fm->negative_dentry_timeout = ffc->negative_dentry_timeout;
WARN_ON(fsc->root);
fsc->root = dget(sb->s_root);
--
2.41.0.185.g7c58973941-goog