On Thu, Dec 03, 2020 at 10:27:24AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> When we allocate a new inode, we often need to add an attribute to
> the inode as part of the create. This can happen as a result of
> needing to add default ACLs or security labels before the inode is
> made visible to userspace.
>
> This is highly inefficient right now. We do the create transaction
> to allocate the inode, then we do an "add attr fork" transaction to
> modify the just created empty inode to set the inode fork offset to
> allow attributes to be stored, then we go and do the attribute
> creation.
>
> This means 3 transactions instead of 1 to allocate an inode, and
> this greatly increases the load on the CIL commit code, resulting in
> excessive contention on the CIL spin locks and performance
> degradation:
>
> 18.99% [kernel] [k] __pv_queued_spin_lock_slowpath
> 3.57% [kernel] [k] do_raw_spin_lock
> 2.51% [kernel] [k] __raw_callee_save___pv_queued_spin_unlock
> 2.48% [kernel] [k] memcpy
> 2.34% [kernel] [k] xfs_log_commit_cil
>
> The typical profile resulting from running fsmark on a selinux enabled
> filesytem is adds this overhead to the create path:
>
...
>
> And fsmark creation rate performance drops by ~25%. The key point to
> note here is that half the additional overhead comes from adding the
> attribute fork to the newly created inode. That's crazy, considering
> we can do this same thing at inode create time with a couple of
> lines of code and no extra overhead.
>
> So, if we know we are going to add an attribute immediately after
> creating the inode, let's just initialise the attribute fork inside
> the create transaction and chop that whole chunk of code out of
> the create fast path. This completely removes the performance
> drop caused by enabling SELinux, and the profile looks like:
>
...
>
> Which indicates the XFS overhead of creating the selinux xattr has
> been halved. This doesn't fix the CIL lock contention problem, just
> means it's not a limiting factor for this workload. Lock contention
> in the security subsystems is going to be an issue soon, though...
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_inode_fork.c | 20 +++++++++++++++-----
> fs/xfs/libxfs/xfs_inode_fork.h | 1 +
> fs/xfs/xfs_inode.c | 24 ++++++++++++++++++++----
> fs/xfs/xfs_inode.h | 5 +++--
> fs/xfs/xfs_iops.c | 10 +++++++++-
> fs/xfs/xfs_qm.c | 2 +-
> fs/xfs/xfs_symlink.c | 2 +-
> 7 files changed, 50 insertions(+), 14 deletions(-)
>
...
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 2bfbcf28b1bd..9ee2e0b4c6fd 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
...
> @@ -918,6 +919,18 @@ xfs_ialloc(
> ASSERT(0);
> }
>
> + /*
> + * If we need to create attributes immediately after allocating the
> + * inode, initialise an empty attribute fork right now. We use the
> + * default fork offset for attributes here as we don't know exactly what
> + * size or how many attributes we might be adding. We can do this safely
> + * here because we know the data fork is completely empty right now.
> + */
> + if (init_attrs) {
> + ip->i_afp = xfs_ifork_alloc(XFS_DINODE_FMT_EXTENTS, 0);
> + ip->i_d.di_forkoff = xfs_default_attroffset(ip) >> 3;
> + }
> +
Seems reasonable in principle, but why not refactor
xfs_bmap_add_attrfork() such that the internals (i.e. everything within
the transaction/ilock code) can be properly reused in both contexts
rather than open-coding (and thus duplicating) a somewhat stripped down
version? At a glance, it looks like there are some subtle differences in
the initial setup of the attr fork for a device node inode, for example.
Brian
> /*
> * Log the new values stuffed into the inode.
> */
> @@ -951,6 +964,7 @@ xfs_dir_ialloc(
> xfs_nlink_t nlink,
> dev_t rdev,
> prid_t prid, /* project id */
> + bool init_attrs,
> xfs_inode_t **ipp) /* pointer to inode; it will be
> locked. */
> {
> @@ -980,7 +994,7 @@ xfs_dir_ialloc(
> * the inode(s) that we've just allocated.
> */
> code = xfs_ialloc(tp, dp, mode, nlink, rdev, prid, &ialloc_context,
> - &ip);
> + init_attrs, &ip);
>
> /*
> * Return an error if we were unable to allocate a new inode.
> @@ -1050,7 +1064,7 @@ xfs_dir_ialloc(
> * this call should always succeed.
> */
> code = xfs_ialloc(tp, dp, mode, nlink, rdev, prid,
> - &ialloc_context, &ip);
> + &ialloc_context, init_attrs, &ip);
>
> /*
> * If we get an error at this point, return to the caller
> @@ -1112,6 +1126,7 @@ xfs_create(
> struct xfs_name *name,
> umode_t mode,
> dev_t rdev,
> + bool init_attrs,
> xfs_inode_t **ipp)
> {
> int is_dir = S_ISDIR(mode);
> @@ -1182,7 +1197,8 @@ xfs_create(
> * entry pointing to them, but a directory also the "." entry
> * pointing to itself.
> */
> - error = xfs_dir_ialloc(&tp, dp, mode, is_dir ? 2 : 1, rdev, prid, &ip);
> + error = xfs_dir_ialloc(&tp, dp, mode, is_dir ? 2 : 1, rdev, prid,
> + init_attrs, &ip);
> if (error)
> goto out_trans_cancel;
>
> @@ -1304,7 +1320,7 @@ xfs_create_tmpfile(
> if (error)
> goto out_trans_cancel;
>
> - error = xfs_dir_ialloc(&tp, dp, mode, 0, 0, prid, &ip);
> + error = xfs_dir_ialloc(&tp, dp, mode, 0, 0, prid, false, &ip);
> if (error)
> goto out_trans_cancel;
>
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 751a3d1d7d84..670dfab334de 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -370,7 +370,8 @@ void xfs_inactive(struct xfs_inode *ip);
> int xfs_lookup(struct xfs_inode *dp, struct xfs_name *name,
> struct xfs_inode **ipp, struct xfs_name *ci_name);
> int xfs_create(struct xfs_inode *dp, struct xfs_name *name,
> - umode_t mode, dev_t rdev, struct xfs_inode **ipp);
> + umode_t mode, dev_t rdev, bool need_xattr,
> + struct xfs_inode **ipp);
> int xfs_create_tmpfile(struct xfs_inode *dp, umode_t mode,
> struct xfs_inode **ipp);
> int xfs_remove(struct xfs_inode *dp, struct xfs_name *name,
> @@ -408,7 +409,7 @@ xfs_extlen_t xfs_get_extsz_hint(struct xfs_inode *ip);
> xfs_extlen_t xfs_get_cowextsz_hint(struct xfs_inode *ip);
>
> int xfs_dir_ialloc(struct xfs_trans **, struct xfs_inode *, umode_t,
> - xfs_nlink_t, dev_t, prid_t,
> + xfs_nlink_t, dev_t, prid_t, bool need_xattr,
> struct xfs_inode **);
>
> static inline int
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 1414ab79eacf..75b44b82ad1f 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -126,6 +126,7 @@ xfs_cleanup_inode(
> xfs_remove(XFS_I(dir), &teardown, XFS_I(inode));
> }
>
> +
> STATIC int
> xfs_generic_create(
> struct inode *dir,
> @@ -161,7 +162,14 @@ xfs_generic_create(
> goto out_free_acl;
>
> if (!tmpfile) {
> - error = xfs_create(XFS_I(dir), &name, mode, rdev, &ip);
> + bool need_xattr = false;
> +
> + if ((IS_ENABLED(CONFIG_SECURITY) && dir->i_sb->s_security) ||
> + default_acl || acl)
> + need_xattr = true;
> +
> + error = xfs_create(XFS_I(dir), &name, mode, rdev,
> + need_xattr, &ip);
> } else {
> error = xfs_create_tmpfile(XFS_I(dir), mode, &ip);
> }
> diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
> index b2a9abee8b2b..45faddfb4234 100644
> --- a/fs/xfs/xfs_qm.c
> +++ b/fs/xfs/xfs_qm.c
> @@ -787,7 +787,7 @@ xfs_qm_qino_alloc(
> return error;
>
> if (need_alloc) {
> - error = xfs_dir_ialloc(&tp, NULL, S_IFREG, 1, 0, 0, ip);
> + error = xfs_dir_ialloc(&tp, NULL, S_IFREG, 1, 0, 0, false, ip);
> if (error) {
> xfs_trans_cancel(tp);
> return error;
> diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
> index 8e88a7ca387e..20919aaea981 100644
> --- a/fs/xfs/xfs_symlink.c
> +++ b/fs/xfs/xfs_symlink.c
> @@ -224,7 +224,7 @@ xfs_symlink(
> * Allocate an inode for the symlink.
> */
> error = xfs_dir_ialloc(&tp, dp, S_IFLNK | (mode & ~S_IFMT), 1, 0,
> - prid, &ip);
> + prid, false, &ip);
> if (error)
> goto out_trans_cancel;
>
> --
> 2.28.0
>
