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5e3f7694b1
and flags with an sxlock. This leads to a significant and measurable performance improvement as a result of access to shared locking for frequent lookup operations, reduced general overhead, and reduced overhead in the event of contention. All of these are imported for threaded applications where simultaneous access to a shared file descriptor array occurs frequently. Kris has reported 2x-4x transaction rate improvements on 8-core MySQL benchmarks; smaller improvements can be expected for many workloads as a result of reduced overhead. - Generally eliminate the distinction between "fast" and regular acquisisition of the filedesc lock; the plan is that they will now all be fast. Change all locking instances to either shared or exclusive locks. - Correct a bug (pointed out by kib) in fdfree() where previously msleep() was called without the mutex held; sx_sleep() is now always called with the sxlock held exclusively. - Universally hold the struct file lock over changes to struct file, rather than the filedesc lock or no lock. Always update the f_ops field last. A further memory barrier is required here in the future (discussed with jhb). - Improve locking and reference management in linux_at(), which fails to properly acquire vnode references before using vnode pointers. Annotate improper use of vn_fullpath(), which will be replaced at a future date. In fcntl(), we conservatively acquire an exclusive lock, even though in some cases a shared lock may be sufficient, which should be revisited. The dropping of the filedesc lock in fdgrowtable() is no longer required as the sxlock can be held over the sleep operation; we should consider removing that (pointed out by attilio). Tested by: kris Discussed with: jhb, kris, attilio, jeff
215 lines
5.3 KiB
C
215 lines
5.3 KiB
C
/*-
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* Copyright (c) 1992, 1993, 1995
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software donated to Berkeley by
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* Jan-Simon Pendry.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)fdesc_vfsops.c 8.4 (Berkeley) 1/21/94
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*
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* $FreeBSD$
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*/
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/*
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* /dev/fd Filesystem
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*/
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/filedesc.h>
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#include <sys/kernel.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/malloc.h>
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#include <sys/mount.h>
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#include <sys/proc.h>
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#include <sys/resourcevar.h>
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#include <sys/vnode.h>
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#include <fs/fdescfs/fdesc.h>
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static MALLOC_DEFINE(M_FDESCMNT, "fdesc_mount", "FDESC mount structure");
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static vfs_cmount_t fdesc_cmount;
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static vfs_mount_t fdesc_mount;
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static vfs_unmount_t fdesc_unmount;
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static vfs_statfs_t fdesc_statfs;
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static vfs_root_t fdesc_root;
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/*
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* Compatibility shim for old mount(2) system call.
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*/
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int
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fdesc_cmount(struct mntarg *ma, void *data, int flags, struct thread *td)
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{
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return kernel_mount(ma, flags);
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}
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/*
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* Mount the per-process file descriptors (/dev/fd)
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*/
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static int
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fdesc_mount(struct mount *mp, struct thread *td)
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{
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int error = 0;
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struct fdescmount *fmp;
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struct vnode *rvp;
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/*
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* Update is a no-op
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*/
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if (mp->mnt_flag & (MNT_UPDATE | MNT_ROOTFS))
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return (EOPNOTSUPP);
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error = fdesc_allocvp(Froot, FD_ROOT, mp, &rvp, td);
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if (error)
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return (error);
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MALLOC(fmp, struct fdescmount *, sizeof(struct fdescmount),
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M_FDESCMNT, M_WAITOK); /* XXX */
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rvp->v_type = VDIR;
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rvp->v_vflag |= VV_ROOT;
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fmp->f_root = rvp;
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/* XXX -- don't mark as local to work around fts() problems */
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/*mp->mnt_flag |= MNT_LOCAL;*/
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mp->mnt_data = (qaddr_t) fmp;
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vfs_getnewfsid(mp);
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vfs_mountedfrom(mp, "fdescfs");
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return (0);
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}
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static int
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fdesc_unmount(mp, mntflags, td)
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struct mount *mp;
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int mntflags;
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struct thread *td;
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{
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int error;
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int flags = 0;
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if (mntflags & MNT_FORCE)
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flags |= FORCECLOSE;
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/*
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* Clear out buffer cache. I don't think we
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* ever get anything cached at this level at the
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* moment, but who knows...
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*
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* There is 1 extra root vnode reference corresponding
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* to f_root.
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*/
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if ((error = vflush(mp, 1, flags, td)) != 0)
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return (error);
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/*
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* Finally, throw away the fdescmount structure
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*/
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free(mp->mnt_data, M_FDESCMNT); /* XXX */
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mp->mnt_data = 0;
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return (0);
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}
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static int
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fdesc_root(mp, flags, vpp, td)
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struct mount *mp;
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int flags;
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struct vnode **vpp;
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struct thread *td;
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{
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struct vnode *vp;
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/*
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* Return locked reference to root.
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*/
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vp = VFSTOFDESC(mp)->f_root;
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VREF(vp);
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vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
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*vpp = vp;
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return (0);
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}
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static int
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fdesc_statfs(mp, sbp, td)
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struct mount *mp;
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struct statfs *sbp;
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struct thread *td;
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{
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struct filedesc *fdp;
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int lim;
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int i;
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int last;
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int freefd;
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/*
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* Compute number of free file descriptors.
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* [ Strange results will ensue if the open file
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* limit is ever reduced below the current number
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* of open files... ]
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*/
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PROC_LOCK(td->td_proc);
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lim = lim_cur(td->td_proc, RLIMIT_NOFILE);
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PROC_UNLOCK(td->td_proc);
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fdp = td->td_proc->p_fd;
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FILEDESC_SLOCK(fdp);
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last = min(fdp->fd_nfiles, lim);
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freefd = 0;
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for (i = fdp->fd_freefile; i < last; i++)
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if (fdp->fd_ofiles[i] == NULL)
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freefd++;
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/*
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* Adjust for the fact that the fdesc array may not
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* have been fully allocated yet.
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*/
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if (fdp->fd_nfiles < lim)
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freefd += (lim - fdp->fd_nfiles);
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FILEDESC_SUNLOCK(fdp);
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sbp->f_flags = 0;
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sbp->f_bsize = DEV_BSIZE;
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sbp->f_iosize = DEV_BSIZE;
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sbp->f_blocks = 2; /* 1K to keep df happy */
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sbp->f_bfree = 0;
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sbp->f_bavail = 0;
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sbp->f_files = lim + 1; /* Allow for "." */
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sbp->f_ffree = freefd; /* See comments above */
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return (0);
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}
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static struct vfsops fdesc_vfsops = {
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.vfs_cmount = fdesc_cmount,
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.vfs_init = fdesc_init,
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.vfs_mount = fdesc_mount,
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.vfs_root = fdesc_root,
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.vfs_statfs = fdesc_statfs,
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.vfs_unmount = fdesc_unmount,
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};
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VFS_SET(fdesc_vfsops, fdescfs, VFCF_SYNTHETIC);
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