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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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4
include/linux/fs.h
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@ -9,6 +9,7 @@
#include <linux/config.h>
#include <linux/limits.h>
#include <linux/ioctl.h>
#include <linux/rcuref.h>
/*
* It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@ -597,12 +598,13 @@ struct file {
spinlock_t f_ep_lock;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
struct rcu_head f_rcuhead;
};
extern spinlock_t files_lock;
#define file_list_lock() spin_lock(&files_lock);
#define file_list_unlock() spin_unlock(&files_lock);
#define get_file(x) atomic_inc(&(x)->f_count)
#define get_file(x) rcuref_inc(&(x)->f_count)
#define file_count(x) atomic_read(&(x)->f_count)
#define MAX_NON_LFS ((1UL<<31) - 1)