| Message ID | 20190829113505.27223-6-david@fromorbit.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | xfs: allocate xattr buffer on demand | expand |
On Thu, Aug 29, 2019 at 09:35:05PM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > When doing file lookups and checking for permissions, we end up in > xfs_get_acl() to see if there are any ACLs on the inode. This > requires and xattr lookup, and to do that we have to supply a buffer > large enough to hold an maximum sized xattr. > > On workloads were we are accessing a wide range of cache cold files > under memory pressure (e.g. NFS fileservers) we end up spending a > lot of time allocating the buffer. The buffer is 64k in length, so > is a contiguous multi-page allocation, and if that then fails we > fall back to vmalloc(). Hence the allocation here is /expensive/ > when we are looking up hundreds of thousands of files a second. > > Initial numbers from a bpf trace show average time in xfs_get_acl() > is ~32us, with ~19us of that in the memory allocation. Note these > are average times, so there are going to be affected by the worst > case allocations more than the common fast case... > > To avoid this, we could just do a "null" lookup to see if the ACL > xattr exists and then only do the allocation if it exists. This, > however, optimises the path for the "no ACL present" case at the > expense of the "acl present" case. i.e. we can halve the time in > xfs_get_acl() for the no acl case (i.e down to ~10-15us), but that > then increases the ACL case by 30% (i.e. up to 40-45us). > > To solve this and speed up both cases, drive the xattr buffer > allocation into the attribute code once we know what the actual > xattr length is. For the no-xattr case, we avoid the allocation > completely, speeding up that case. For the common ACL case, we'll > end up with a fast heap allocation (because it'll be smaller than a > page), and only for the rarer "we have a remote xattr" will we have > a multi-page allocation occur. Hence the common ACL case will be > much faster, too. > > Signed-off-by: Dave Chinner <dchinner@redhat.com> Looks ok, will throw this (and the dir speedup series) at the testing machine... Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> --D > --- > fs/xfs/libxfs/xfs_attr.c | 42 ++++++++++++++++++++++++++++++----- > fs/xfs/libxfs/xfs_attr.h | 6 +++-- > fs/xfs/libxfs/xfs_attr_leaf.c | 6 +++++ > fs/xfs/libxfs/xfs_da_btree.h | 4 +++- > fs/xfs/xfs_acl.c | 12 ++++------ > fs/xfs/xfs_ioctl.c | 2 +- > fs/xfs/xfs_xattr.c | 2 +- > 7 files changed, 55 insertions(+), 19 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c > index 4773eef9d3de..510ca6974604 100644 > --- a/fs/xfs/libxfs/xfs_attr.c > +++ b/fs/xfs/libxfs/xfs_attr.c > @@ -118,12 +118,28 @@ xfs_attr_get_ilocked( > return xfs_attr_node_get(args); > } > > -/* Retrieve an extended attribute by name, and its value. */ > +/* > + * Retrieve an extended attribute by name, and its value if requested. > + * > + * If ATTR_KERNOVAL is set in @flags, then the caller does not want the value, > + * just an indication whether the attribute exists and the size of the value if > + * it exists. The size is returned in @valuelenp, > + * > + * If the attribute is found, but exceeds the size limit set by the caller in > + * @valuelenp, return -ERANGE with the size of the attribute that was found in > + * @valuelenp. > + * > + * If ATTR_ALLOC is set in @flags, allocate the buffer for the value after > + * existence of the attribute has been determined. On success, return that > + * buffer to the caller and leave them to free it. On failure, free any > + * allocated buffer and ensure the buffer pointer returned to the caller is > + * null. > + */ > int > xfs_attr_get( > struct xfs_inode *ip, > const unsigned char *name, > - unsigned char *value, > + unsigned char **value, > int *valuelenp, > int flags) > { > @@ -131,6 +147,8 @@ xfs_attr_get( > uint lock_mode; > int error; > > + ASSERT((flags & (ATTR_ALLOC | ATTR_KERNOVAL)) || *value); > + > XFS_STATS_INC(ip->i_mount, xs_attr_get); > > if (XFS_FORCED_SHUTDOWN(ip->i_mount)) > @@ -140,17 +158,29 @@ xfs_attr_get( > if (error) > return error; > > - args.value = value; > - args.valuelen = *valuelenp; > /* Entirely possible to look up a name which doesn't exist */ > args.op_flags = XFS_DA_OP_OKNOENT; > + if (flags & ATTR_ALLOC) > + args.op_flags |= XFS_DA_OP_ALLOCVAL; > + else > + args.value = *value; > + args.valuelen = *valuelenp; > > lock_mode = xfs_ilock_attr_map_shared(ip); > error = xfs_attr_get_ilocked(ip, &args); > xfs_iunlock(ip, lock_mode); > - > *valuelenp = args.valuelen; > - return error; > + > + /* on error, we have to clean up allocated value buffers */ > + if (error) { > + if (flags & ATTR_ALLOC) { > + kmem_free(args.value); > + *value = NULL; > + } > + return error; > + } > + *value = args.value; > + return 0; > } > > /* > diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h > index ff28ebf3b635..94badfa1743e 100644 > --- a/fs/xfs/libxfs/xfs_attr.h > +++ b/fs/xfs/libxfs/xfs_attr.h > @@ -37,6 +37,7 @@ struct xfs_attr_list_context; > #define ATTR_KERNOVAL 0x2000 /* [kernel] get attr size only, not value */ > > #define ATTR_INCOMPLETE 0x4000 /* [kernel] return INCOMPLETE attr keys */ > +#define ATTR_ALLOC 0x8000 /* allocate xattr buffer on demand */ > > #define XFS_ATTR_FLAGS \ > { ATTR_DONTFOLLOW, "DONTFOLLOW" }, \ > @@ -47,7 +48,8 @@ struct xfs_attr_list_context; > { ATTR_REPLACE, "REPLACE" }, \ > { ATTR_KERNOTIME, "KERNOTIME" }, \ > { ATTR_KERNOVAL, "KERNOVAL" }, \ > - { ATTR_INCOMPLETE, "INCOMPLETE" } > + { ATTR_INCOMPLETE, "INCOMPLETE" }, \ > + { ATTR_ALLOC, "ALLOC" } > > /* > * The maximum size (into the kernel or returned from the kernel) of an > @@ -143,7 +145,7 @@ int xfs_attr_list_int(struct xfs_attr_list_context *); > int xfs_inode_hasattr(struct xfs_inode *ip); > int xfs_attr_get_ilocked(struct xfs_inode *ip, struct xfs_da_args *args); > int xfs_attr_get(struct xfs_inode *ip, const unsigned char *name, > - unsigned char *value, int *valuelenp, int flags); > + unsigned char **value, int *valuelenp, int flags); > int xfs_attr_set(struct xfs_inode *dp, const unsigned char *name, > unsigned char *value, int valuelen, int flags); > int xfs_attr_set_args(struct xfs_da_args *args); > diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c > index f6a595e76343..b9f019603d0b 100644 > --- a/fs/xfs/libxfs/xfs_attr_leaf.c > +++ b/fs/xfs/libxfs/xfs_attr_leaf.c > @@ -414,6 +414,12 @@ xfs_attr_copy_value( > args->valuelen = valuelen; > return -ERANGE; > } > + > + if (args->op_flags & XFS_DA_OP_ALLOCVAL) { > + args->value = kmem_alloc_large(valuelen, 0); > + if (!args->value) > + return -ENOMEM; > + } > args->valuelen = valuelen; > > /* remote block xattr requires IO for copy-in */ > diff --git a/fs/xfs/libxfs/xfs_da_btree.h b/fs/xfs/libxfs/xfs_da_btree.h > index 84dd865b6c3d..ae0bbd20d9ca 100644 > --- a/fs/xfs/libxfs/xfs_da_btree.h > +++ b/fs/xfs/libxfs/xfs_da_btree.h > @@ -81,13 +81,15 @@ typedef struct xfs_da_args { > #define XFS_DA_OP_ADDNAME 0x0004 /* this is an add operation */ > #define XFS_DA_OP_OKNOENT 0x0008 /* lookup/add op, ENOENT ok, else die */ > #define XFS_DA_OP_CILOOKUP 0x0010 /* lookup to return CI name if found */ > +#define XFS_DA_OP_ALLOCVAL 0x0020 /* lookup to alloc buffer if found */ > > #define XFS_DA_OP_FLAGS \ > { XFS_DA_OP_JUSTCHECK, "JUSTCHECK" }, \ > { XFS_DA_OP_RENAME, "RENAME" }, \ > { XFS_DA_OP_ADDNAME, "ADDNAME" }, \ > { XFS_DA_OP_OKNOENT, "OKNOENT" }, \ > - { XFS_DA_OP_CILOOKUP, "CILOOKUP" } > + { XFS_DA_OP_CILOOKUP, "CILOOKUP" }, \ > + { XFS_DA_OP_ALLOCVAL, "ALLOCVAL" } > > /* > * Storage for holding state during Btree searches and split/join ops. > diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c > index 86c0697870a5..96d7071cfa46 100644 > --- a/fs/xfs/xfs_acl.c > +++ b/fs/xfs/xfs_acl.c > @@ -112,7 +112,7 @@ xfs_get_acl(struct inode *inode, int type) > { > struct xfs_inode *ip = XFS_I(inode); > struct posix_acl *acl = NULL; > - struct xfs_acl *xfs_acl; > + struct xfs_acl *xfs_acl = NULL; > unsigned char *ea_name; > int error; > int len; > @@ -135,12 +135,8 @@ xfs_get_acl(struct inode *inode, int type) > * go out to the disk. > */ > len = XFS_ACL_MAX_SIZE(ip->i_mount); > - xfs_acl = kmem_zalloc_large(len, 0); > - if (!xfs_acl) > - return ERR_PTR(-ENOMEM); > - > - error = xfs_attr_get(ip, ea_name, (unsigned char *)xfs_acl, > - &len, ATTR_ROOT); > + error = xfs_attr_get(ip, ea_name, (unsigned char **)&xfs_acl, &len, > + ATTR_ALLOC | ATTR_ROOT); > if (error) { > /* > * If the attribute doesn't exist make sure we have a negative > @@ -151,8 +147,8 @@ xfs_get_acl(struct inode *inode, int type) > } else { > acl = xfs_acl_from_disk(xfs_acl, len, > XFS_ACL_MAX_ENTRIES(ip->i_mount)); > + kmem_free(xfs_acl); > } > - kmem_free(xfs_acl); > return acl; > } > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c > index 9ea51664932e..6ad63b57b6ca 100644 > --- a/fs/xfs/xfs_ioctl.c > +++ b/fs/xfs/xfs_ioctl.c > @@ -438,7 +438,7 @@ xfs_attrmulti_attr_get( > if (!kbuf) > return -ENOMEM; > > - error = xfs_attr_get(XFS_I(inode), name, kbuf, (int *)len, flags); > + error = xfs_attr_get(XFS_I(inode), name, &kbuf, (int *)len, flags); > if (error) > goto out_kfree; > > diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c > index 3123b5aaad2a..cb895b1df5e4 100644 > --- a/fs/xfs/xfs_xattr.c > +++ b/fs/xfs/xfs_xattr.c > @@ -30,7 +30,7 @@ xfs_xattr_get(const struct xattr_handler *handler, struct dentry *unused, > value = NULL; > } > > - error = xfs_attr_get(ip, (unsigned char *)name, value, &asize, xflags); > + error = xfs_attr_get(ip, name, (unsigned char **)&value, &asize, xflags); > if (error) > return error; > return asize; > -- > 2.23.0.rc1 >
On Thu, Aug 29, 2019 at 09:35:05PM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > When doing file lookups and checking for permissions, we end up in > xfs_get_acl() to see if there are any ACLs on the inode. This > requires and xattr lookup, and to do that we have to supply a buffer > large enough to hold an maximum sized xattr. > > On workloads were we are accessing a wide range of cache cold files > under memory pressure (e.g. NFS fileservers) we end up spending a > lot of time allocating the buffer. The buffer is 64k in length, so > is a contiguous multi-page allocation, and if that then fails we > fall back to vmalloc(). Hence the allocation here is /expensive/ > when we are looking up hundreds of thousands of files a second. > > Initial numbers from a bpf trace show average time in xfs_get_acl() > is ~32us, with ~19us of that in the memory allocation. Note these > are average times, so there are going to be affected by the worst > case allocations more than the common fast case... > > To avoid this, we could just do a "null" lookup to see if the ACL > xattr exists and then only do the allocation if it exists. This, > however, optimises the path for the "no ACL present" case at the > expense of the "acl present" case. i.e. we can halve the time in > xfs_get_acl() for the no acl case (i.e down to ~10-15us), but that > then increases the ACL case by 30% (i.e. up to 40-45us). > > To solve this and speed up both cases, drive the xattr buffer > allocation into the attribute code once we know what the actual > xattr length is. For the no-xattr case, we avoid the allocation > completely, speeding up that case. For the common ACL case, we'll > end up with a fast heap allocation (because it'll be smaller than a > page), and only for the rarer "we have a remote xattr" will we have > a multi-page allocation occur. Hence the common ACL case will be > much faster, too. > > Signed-off-by: Dave Chinner <dchinner@redhat.com> Looks good, Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c index 4773eef9d3de..510ca6974604 100644 --- a/fs/xfs/libxfs/xfs_attr.c +++ b/fs/xfs/libxfs/xfs_attr.c @@ -118,12 +118,28 @@ xfs_attr_get_ilocked( return xfs_attr_node_get(args); } -/* Retrieve an extended attribute by name, and its value. */ +/* + * Retrieve an extended attribute by name, and its value if requested. + * + * If ATTR_KERNOVAL is set in @flags, then the caller does not want the value, + * just an indication whether the attribute exists and the size of the value if + * it exists. The size is returned in @valuelenp, + * + * If the attribute is found, but exceeds the size limit set by the caller in + * @valuelenp, return -ERANGE with the size of the attribute that was found in + * @valuelenp. + * + * If ATTR_ALLOC is set in @flags, allocate the buffer for the value after + * existence of the attribute has been determined. On success, return that + * buffer to the caller and leave them to free it. On failure, free any + * allocated buffer and ensure the buffer pointer returned to the caller is + * null. + */ int xfs_attr_get( struct xfs_inode *ip, const unsigned char *name, - unsigned char *value, + unsigned char **value, int *valuelenp, int flags) { @@ -131,6 +147,8 @@ xfs_attr_get( uint lock_mode; int error; + ASSERT((flags & (ATTR_ALLOC | ATTR_KERNOVAL)) || *value); + XFS_STATS_INC(ip->i_mount, xs_attr_get); if (XFS_FORCED_SHUTDOWN(ip->i_mount)) @@ -140,17 +158,29 @@ xfs_attr_get( if (error) return error; - args.value = value; - args.valuelen = *valuelenp; /* Entirely possible to look up a name which doesn't exist */ args.op_flags = XFS_DA_OP_OKNOENT; + if (flags & ATTR_ALLOC) + args.op_flags |= XFS_DA_OP_ALLOCVAL; + else + args.value = *value; + args.valuelen = *valuelenp; lock_mode = xfs_ilock_attr_map_shared(ip); error = xfs_attr_get_ilocked(ip, &args); xfs_iunlock(ip, lock_mode); - *valuelenp = args.valuelen; - return error; + + /* on error, we have to clean up allocated value buffers */ + if (error) { + if (flags & ATTR_ALLOC) { + kmem_free(args.value); + *value = NULL; + } + return error; + } + *value = args.value; + return 0; } /* diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h index ff28ebf3b635..94badfa1743e 100644 --- a/fs/xfs/libxfs/xfs_attr.h +++ b/fs/xfs/libxfs/xfs_attr.h @@ -37,6 +37,7 @@ struct xfs_attr_list_context; #define ATTR_KERNOVAL 0x2000 /* [kernel] get attr size only, not value */ #define ATTR_INCOMPLETE 0x4000 /* [kernel] return INCOMPLETE attr keys */ +#define ATTR_ALLOC 0x8000 /* allocate xattr buffer on demand */ #define XFS_ATTR_FLAGS \ { ATTR_DONTFOLLOW, "DONTFOLLOW" }, \ @@ -47,7 +48,8 @@ struct xfs_attr_list_context; { ATTR_REPLACE, "REPLACE" }, \ { ATTR_KERNOTIME, "KERNOTIME" }, \ { ATTR_KERNOVAL, "KERNOVAL" }, \ - { ATTR_INCOMPLETE, "INCOMPLETE" } + { ATTR_INCOMPLETE, "INCOMPLETE" }, \ + { ATTR_ALLOC, "ALLOC" } /* * The maximum size (into the kernel or returned from the kernel) of an @@ -143,7 +145,7 @@ int xfs_attr_list_int(struct xfs_attr_list_context *); int xfs_inode_hasattr(struct xfs_inode *ip); int xfs_attr_get_ilocked(struct xfs_inode *ip, struct xfs_da_args *args); int xfs_attr_get(struct xfs_inode *ip, const unsigned char *name, - unsigned char *value, int *valuelenp, int flags); + unsigned char **value, int *valuelenp, int flags); int xfs_attr_set(struct xfs_inode *dp, const unsigned char *name, unsigned char *value, int valuelen, int flags); int xfs_attr_set_args(struct xfs_da_args *args); diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c index f6a595e76343..b9f019603d0b 100644 --- a/fs/xfs/libxfs/xfs_attr_leaf.c +++ b/fs/xfs/libxfs/xfs_attr_leaf.c @@ -414,6 +414,12 @@ xfs_attr_copy_value( args->valuelen = valuelen; return -ERANGE; } + + if (args->op_flags & XFS_DA_OP_ALLOCVAL) { + args->value = kmem_alloc_large(valuelen, 0); + if (!args->value) + return -ENOMEM; + } args->valuelen = valuelen; /* remote block xattr requires IO for copy-in */ diff --git a/fs/xfs/libxfs/xfs_da_btree.h b/fs/xfs/libxfs/xfs_da_btree.h index 84dd865b6c3d..ae0bbd20d9ca 100644 --- a/fs/xfs/libxfs/xfs_da_btree.h +++ b/fs/xfs/libxfs/xfs_da_btree.h @@ -81,13 +81,15 @@ typedef struct xfs_da_args { #define XFS_DA_OP_ADDNAME 0x0004 /* this is an add operation */ #define XFS_DA_OP_OKNOENT 0x0008 /* lookup/add op, ENOENT ok, else die */ #define XFS_DA_OP_CILOOKUP 0x0010 /* lookup to return CI name if found */ +#define XFS_DA_OP_ALLOCVAL 0x0020 /* lookup to alloc buffer if found */ #define XFS_DA_OP_FLAGS \ { XFS_DA_OP_JUSTCHECK, "JUSTCHECK" }, \ { XFS_DA_OP_RENAME, "RENAME" }, \ { XFS_DA_OP_ADDNAME, "ADDNAME" }, \ { XFS_DA_OP_OKNOENT, "OKNOENT" }, \ - { XFS_DA_OP_CILOOKUP, "CILOOKUP" } + { XFS_DA_OP_CILOOKUP, "CILOOKUP" }, \ + { XFS_DA_OP_ALLOCVAL, "ALLOCVAL" } /* * Storage for holding state during Btree searches and split/join ops. diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c index 86c0697870a5..96d7071cfa46 100644 --- a/fs/xfs/xfs_acl.c +++ b/fs/xfs/xfs_acl.c @@ -112,7 +112,7 @@ xfs_get_acl(struct inode *inode, int type) { struct xfs_inode *ip = XFS_I(inode); struct posix_acl *acl = NULL; - struct xfs_acl *xfs_acl; + struct xfs_acl *xfs_acl = NULL; unsigned char *ea_name; int error; int len; @@ -135,12 +135,8 @@ xfs_get_acl(struct inode *inode, int type) * go out to the disk. */ len = XFS_ACL_MAX_SIZE(ip->i_mount); - xfs_acl = kmem_zalloc_large(len, 0); - if (!xfs_acl) - return ERR_PTR(-ENOMEM); - - error = xfs_attr_get(ip, ea_name, (unsigned char *)xfs_acl, - &len, ATTR_ROOT); + error = xfs_attr_get(ip, ea_name, (unsigned char **)&xfs_acl, &len, + ATTR_ALLOC | ATTR_ROOT); if (error) { /* * If the attribute doesn't exist make sure we have a negative @@ -151,8 +147,8 @@ xfs_get_acl(struct inode *inode, int type) } else { acl = xfs_acl_from_disk(xfs_acl, len, XFS_ACL_MAX_ENTRIES(ip->i_mount)); + kmem_free(xfs_acl); } - kmem_free(xfs_acl); return acl; } diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c index 9ea51664932e..6ad63b57b6ca 100644 --- a/fs/xfs/xfs_ioctl.c +++ b/fs/xfs/xfs_ioctl.c @@ -438,7 +438,7 @@ xfs_attrmulti_attr_get( if (!kbuf) return -ENOMEM; - error = xfs_attr_get(XFS_I(inode), name, kbuf, (int *)len, flags); + error = xfs_attr_get(XFS_I(inode), name, &kbuf, (int *)len, flags); if (error) goto out_kfree; diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c index 3123b5aaad2a..cb895b1df5e4 100644 --- a/fs/xfs/xfs_xattr.c +++ b/fs/xfs/xfs_xattr.c @@ -30,7 +30,7 @@ xfs_xattr_get(const struct xattr_handler *handler, struct dentry *unused, value = NULL; } - error = xfs_attr_get(ip, (unsigned char *)name, value, &asize, xflags); + error = xfs_attr_get(ip, name, (unsigned char **)&value, &asize, xflags); if (error) return error; return asize;