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[PATCH] files: files struct with RCU

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Patch to eliminate struct files_struct.file_lock spinlock on the reader side
and use rcu refcounting rcuref_xxx api for the f_count refcounter.  The
updates to the fdtable are done by allocating a new fdtable structure and
setting files->fdt to point to the new structure.  The fdtable structure is
protected by RCU thereby allowing lock-free lookup.  For fd arrays/sets that
are vmalloced, we use keventd to free them since RCU callbacks can't sleep.  A
global list of fdtable to be freed is not scalable, so we use a per-cpu list.
If keventd is already handling the current cpu's work, we use a timer to defer
queueing of that work.

Since the last publication, this patch has been re-written to avoid using
explicit memory barriers and use rcu_assign_pointer(), rcu_dereference()
premitives instead.  This required that the fd information is kept in a
separate structure (fdtable) and updated atomically.

Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Dipankar Sarma
2005-09-09 13:04:13 -07:00
committed by Linus Torvalds
parent 6e72ad2c58
commit ab2af1f500
10 changed files with 354 additions and 175 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
kernel/exit.c
View File

@@ -411,15 +411,16 @@ void fastcall put_files_struct(struct files_struct *files)
close_files(files);
/*
* Free the fd and fdset arrays if we expanded them.
* If the fdtable was embedded, pass files for freeing
* at the end of the RCU grace period. Otherwise,
* you can free files immediately.
*/
fdt = files_fdtable(files);
if (fdt->fd != &files->fd_array[0])
free_fd_array(fdt->fd, fdt->max_fds);
if (fdt->max_fdset > __FD_SETSIZE) {
free_fdset(fdt->open_fds, fdt->max_fdset);
free_fdset(fdt->close_on_exec, fdt->max_fdset);
}
kmem_cache_free(files_cachep, files);
if (fdt == &files->fdtab)
fdt->free_files = files;
else
kmem_cache_free(files_cachep, files);
free_fdtable(fdt);
}
}

23
kernel/fork.c
View File

@@ -35,6 +35,7 @@
#include <linux/syscalls.h>
#include <linux/jiffies.h>
#include <linux/futex.h>
#include <linux/rcupdate.h>
#include <linux/ptrace.h>
#include <linux/mount.h>
#include <linux/audit.h>
@@ -565,13 +566,12 @@ static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
return 0;
}
static int count_open_files(struct files_struct *files, int size)
static int count_open_files(struct fdtable *fdt)
{
int size = fdt->max_fdset;
int i;
struct fdtable *fdt;
/* Find the last open fd */
fdt = files_fdtable(files);
for (i = size/(8*sizeof(long)); i > 0; ) {
if (fdt->open_fds->fds_bits[--i])
break;
@@ -592,13 +592,17 @@ static struct files_struct *alloc_files(void)
atomic_set(&newf->count, 1);
spin_lock_init(&newf->file_lock);
fdt = files_fdtable(newf);
fdt = &newf->fdtab;
fdt->next_fd = 0;
fdt->max_fds = NR_OPEN_DEFAULT;
fdt->max_fdset = __FD_SETSIZE;
fdt->close_on_exec = &newf->close_on_exec_init;
fdt->open_fds = &newf->open_fds_init;
fdt->fd = &newf->fd_array[0];
INIT_RCU_HEAD(&fdt->rcu);
fdt->free_files = NULL;
fdt->next = NULL;
rcu_assign_pointer(newf->fdt, fdt);
out:
return newf;
}
@@ -637,7 +641,7 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
old_fdt = files_fdtable(oldf);
new_fdt = files_fdtable(newf);
size = old_fdt->max_fdset;
open_files = count_open_files(oldf, old_fdt->max_fdset);
open_files = count_open_files(old_fdt);
expand = 0;
/*
@@ -661,7 +665,14 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
spin_unlock(&newf->file_lock);
if (error < 0)
goto out_release;
new_fdt = files_fdtable(newf);
/*
* Reacquire the oldf lock and a pointer to its fd table
* who knows it may have a new bigger fd table. We need
* the latest pointer.
*/
spin_lock(&oldf->file_lock);
old_fdt = files_fdtable(oldf);
}
old_fds = old_fdt->fd;
@@ -683,7 +694,7 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
*/
FD_CLR(open_files - i, new_fdt->open_fds);
}
*new_fds++ = f;
rcu_assign_pointer(*new_fds++, f);
}
spin_unlock(&oldf->file_lock);