[patch 3/3] epoll optimizations and cleanups ...

[patch 3/3] epoll optimizations and cleanups ...

[Davide Libenzi]

This patch cuts out lots of code from epoll, by reusing the anonymous 
inode source of patch 2/3.



Signed-off-by: Davide Libenzi <davidel@xmailserver.org>



- Davide



eventpoll.c |  174 +-----------------------------------------------------------
1 file changed, 3 insertions(+), 171 deletions(-)



Index: linux-2.6.20.ep2/fs/eventpoll.c
===================================================================
--- linux-2.6.20.ep2.orig/fs/eventpoll.c	2007-03-06 11:09:00.000000000 -0800
+++ linux-2.6.20.ep2/fs/eventpoll.c	2007-03-06 11:12:43.000000000 -0800
@@ -35,6 +35,7 @@
 #include <linux/mount.h>
 #include <linux/bitops.h>
 #include <linux/mutex.h>
+#include <linux/anon_inodes.h>
 #include <asm/uaccess.h>
 #include <asm/system.h>
 #include <asm/io.h>
@@ -76,8 +77,6 @@
  */
 
 
-#define EVENTPOLLFS_MAGIC 0x03111965 /* My birthday should work for this :) */
-
 #define DEBUG_EPOLL 0
 
 #if DEBUG_EPOLL > 0
@@ -229,8 +228,6 @@
 
 static void ep_poll_safewake_init(struct poll_safewake *psw);
 static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq);
-static int ep_getfd(int *efd, struct inode **einode, struct file **efile,
-		    struct eventpoll *ep);
 static int ep_alloc(struct eventpoll **pep);
 static void ep_free(struct eventpoll *ep);
 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd);
@@ -256,11 +253,6 @@
 			      int maxevents);
 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
 		   int maxevents, long timeout);
-static int eventpollfs_delete_dentry(struct dentry *dentry);
-static struct inode *ep_eventpoll_inode(void);
-static int eventpollfs_get_sb(struct file_system_type *fs_type,
-			      int flags, const char *dev_name,
-			      void *data, struct vfsmount *mnt);
 
 /*
  * This semaphore is used to serialize ep_free() and eventpoll_release_file().
@@ -276,30 +268,12 @@
 /* Slab cache used to allocate "struct eppoll_entry" */
 static struct kmem_cache *pwq_cache __read_mostly;
 
-/* Virtual fs used to allocate inodes for eventpoll files */
-static struct vfsmount *eventpoll_mnt __read_mostly;
-
 /* File callbacks that implement the eventpoll file behaviour */
 static const struct file_operations eventpoll_fops = {
 	.release	= ep_eventpoll_close,
 	.poll		= ep_eventpoll_poll
 };
 
-/*
- * This is used to register the virtual file system from where
- * eventpoll inodes are allocated.
- */
-static struct file_system_type eventpoll_fs_type = {
-	.name		= "eventpollfs",
-	.get_sb		= eventpollfs_get_sb,
-	.kill_sb	= kill_anon_super,
-};
-
-/* Very basic directory entry operations for the eventpoll virtual file system */
-static struct dentry_operations eventpollfs_dentry_operations = {
-	.d_delete	= eventpollfs_delete_dentry,
-};
-
 
 
 /* Fast test to see if the file is an evenpoll file */
@@ -496,7 +470,8 @@
 	 * Creates all the items needed to setup an eventpoll file. That is,
 	 * a file structure, and inode and a free file descriptor.
 	 */
-	error = ep_getfd(&fd, &inode, &file, ep);
+	error = aino_getfd(&fd, &inode, &file, "[eventpoll]",
+			   &eventpoll_fops, ep);
 	if (error)
 		goto eexit_2;
 
@@ -726,82 +701,6 @@
 #endif /* #ifdef TIF_RESTORE_SIGMASK */
 
 
-/*
- * Creates the file descriptor to be used by the epoll interface.
- */
-static int ep_getfd(int *efd, struct inode **einode, struct file **efile,
-		    struct eventpoll *ep)
-{
-	struct qstr this;
-	char name[32];
-	struct dentry *dentry;
-	struct inode *inode;
-	struct file *file;
-	int error, fd;
-
-	/* Get an ready to use file */
-	error = -ENFILE;
-	file = get_empty_filp();
-	if (!file)
-		goto eexit_1;
-
-	/* Allocates an inode from the eventpoll file system */
-	inode = ep_eventpoll_inode();
-	if (IS_ERR(inode)) {
-		error = PTR_ERR(inode);
-		goto eexit_2;
-	}
-
-	/* Allocates a free descriptor to plug the file onto */
-	error = get_unused_fd();
-	if (error < 0)
-		goto eexit_3;
-	fd = error;
-
-	/*
-	 * Link the inode to a directory entry by creating a unique name
-	 * using the inode number.
-	 */
-	error = -ENOMEM;
-	sprintf(name, "[%lu]", inode->i_ino);
-	this.name = name;
-	this.len = strlen(name);
-	this.hash = inode->i_ino;
-	dentry = d_alloc(eventpoll_mnt->mnt_sb->s_root, &this);
-	if (!dentry)
-		goto eexit_4;
-	dentry->d_op = &eventpollfs_dentry_operations;
-	d_add(dentry, inode);
-	file->f_path.mnt = mntget(eventpoll_mnt);
-	file->f_path.dentry = dentry;
-	file->f_mapping = inode->i_mapping;
-
-	file->f_pos = 0;
-	file->f_flags = O_RDONLY;
-	file->f_op = &eventpoll_fops;
-	file->f_mode = FMODE_READ;
-	file->f_version = 0;
-	file->private_data = ep;
-
-	/* Install the new setup file into the allocated fd. */
-	fd_install(fd, file);
-
-	*efd = fd;
-	*einode = inode;
-	*efile = file;
-	return 0;
-
-eexit_4:
-	put_unused_fd(fd);
-eexit_3:
-	iput(inode);
-eexit_2:
-	put_filp(file);
-eexit_1:
-	return error;
-}
-
-
 static int ep_alloc(struct eventpoll **pep)
 {
 	struct eventpoll *ep = kzalloc(sizeof(*ep), GFP_KERNEL);
@@ -1553,54 +1452,8 @@
 }
 
 
-static int eventpollfs_delete_dentry(struct dentry *dentry)
-{
-
-	return 1;
-}
-
-
-static struct inode *ep_eventpoll_inode(void)
-{
-	int error = -ENOMEM;
-	struct inode *inode = new_inode(eventpoll_mnt->mnt_sb);
-
-	if (!inode)
-		goto eexit_1;
-
-	inode->i_fop = &eventpoll_fops;
-
-	/*
-	 * Mark the inode dirty from the very beginning,
-	 * that way it will never be moved to the dirty
-	 * list because mark_inode_dirty() will think
-	 * that it already _is_ on the dirty list.
-	 */
-	inode->i_state = I_DIRTY;
-	inode->i_mode = S_IRUSR | S_IWUSR;
-	inode->i_uid = current->fsuid;
-	inode->i_gid = current->fsgid;
-	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
-	return inode;
-
-eexit_1:
-	return ERR_PTR(error);
-}
-
-
-static int
-eventpollfs_get_sb(struct file_system_type *fs_type, int flags,
-		   const char *dev_name, void *data, struct vfsmount *mnt)
-{
-	return get_sb_pseudo(fs_type, "eventpoll:", NULL, EVENTPOLLFS_MAGIC,
-			     mnt);
-}
-
-
 static int __init eventpoll_init(void)
 {
-	int error;
-
 	mutex_init(&epmutex);
 
 	/* Initialize the structure used to perform safe poll wait head wake ups */
@@ -1616,34 +1469,13 @@
 			sizeof(struct eppoll_entry), 0,
 			EPI_SLAB_DEBUG|SLAB_PANIC, NULL, NULL);
 
-	/*
-	 * Register the virtual file system that will be the source of inodes
-	 * for the eventpoll files
-	 */
-	error = register_filesystem(&eventpoll_fs_type);
-	if (error)
-		goto epanic;
-
-	/* Mount the above commented virtual file system */
-	eventpoll_mnt = kern_mount(&eventpoll_fs_type);
-	error = PTR_ERR(eventpoll_mnt);
-	if (IS_ERR(eventpoll_mnt))
-		goto epanic;
-
-	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: successfully initialized.\n",
-			current));
 	return 0;
-
-epanic:
-	panic("eventpoll_init() failed\n");
 }
 
 
 static void __exit eventpoll_exit(void)
 {
 	/* Undo all operations done inside eventpoll_init() */
-	unregister_filesystem(&eventpoll_fs_type);
-	mntput(eventpoll_mnt);
 	kmem_cache_destroy(pwq_cache);
 	kmem_cache_destroy(epi_cache);
 }

epoll optimizations

[Howard Chu]

Something I tripped over recently, that might be nice to change... HANGUP 
events are always reported, and apparently can't be turned off. In 
level-triggered mode, if your event loop treats Hangups as lower priority than 
read/write events, an outstanding Hangup will continue to be signaled every 
time you call epoll_wait() until it's finally disposed of. It would be nice if 
Hangups were always oneshot events, regardless of whether the FD was 
configured level, edge, or oneshot. Certainly we know that the *cause* of a 
Hangup can only happen once on any descriptor, so it makes no sense for it to 
be reported more than once.

-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/

Re: epoll optimizations

[Davide Libenzi]

On Thu, 29 Jan 2009, Howard Chu wrote:

> Something I tripped over recently, that might be nice to change... HANGUP
> events are always reported, and apparently can't be turned off. In
> level-triggered mode, if your event loop treats Hangups as lower priority than
> read/write events, an outstanding Hangup will continue to be signaled every
> time you call epoll_wait() until it's finally disposed of. It would be nice if
> Hangups were always oneshot events, regardless of whether the FD was
> configured level, edge, or oneshot. Certainly we know that the *cause* of a
> Hangup can only happen once on any descriptor, so it makes no sense for it to
> be reported more than once.

Since epoll does not have the concept of priority, that means that you 
have to scan the whole array of returned events anyway. It is sufficient 
that when you notice a POLLHUP, you do a quick handling with a simple 
epoll_ctl(DEL), append the fd to a lazy-handling queue, and take care of 
it when time comes.



- Davide