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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
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3
fs/aio.c
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@@ -29,6 +29,7 @@
#include <linux/highmem.h>
#include <linux/workqueue.h>
#include <linux/security.h>
#include <linux/rcuref.h>
#include <asm/kmap_types.h>
#include <asm/uaccess.h>
@@ -499,7 +500,7 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
/* Must be done under the lock to serialise against cancellation.
* Call this aio_fput as it duplicates fput via the fput_work.
*/
if (unlikely(atomic_dec_and_test(&req->ki_filp->f_count))) {
if (unlikely(rcuref_dec_and_test(&req->ki_filp->f_count))) {
get_ioctx(ctx);
spin_lock(&fput_lock);
list_add(&req->ki_list, &fput_head);