From 8b5882c50759d4178c3bbfcd898bf0062c555967 Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Fri, 15 Nov 2019 17:16:23 -0500 Subject: [PATCH] xfs: allocate xattr buffer on demand Source kernel commit: ddbca70cc45c0ac97ff6d9529e45f10b8ae73ad4 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 Reviewed-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong Signed-off-by: Eric Sandeen i_mount, xs_attr_get); if (XFS_FORCED_SHUTDOWN(ip->i_mount)) @@ -139,17 +157,29 @@ 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/libxfs/xfs_attr.h b/libxfs/xfs_attr.h index ff28ebf3b..94badfa17 100644 --- a/libxfs/xfs_attr.h +++ b/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/libxfs/xfs_attr_leaf.c b/libxfs/xfs_attr_leaf.c index 0ed2478a3..a91e5e1ed 100644 --- a/libxfs/xfs_attr_leaf.c +++ b/libxfs/xfs_attr_leaf.c @@ -410,6 +410,12 @@ 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/libxfs/xfs_da_btree.h b/libxfs/xfs_da_btree.h index 84dd865b6..ae0bbd20d 100644 --- a/libxfs/xfs_da_btree.h +++ b/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. -- 2.47.2