linux-kernel - [RFC 10/10] fs/devpts: use tida for id allocation

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Date:   Thu,  8 Dec 2016 02:23:05 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [RFC 10/10] fs/devpts: use tida for id allocation

Using the newly introduced tida for allocating pty indexes saves
around 16KB of runtime memory. Since tida does it's own internal
locking, we don't need to protect it with the &allocated_ptys_lock and
do the whole "preallocate outside lock, loop if we're extremely
unlucky", thus allowing us simplify devpts_new_index somewhat.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 fs/devpts/inode.c | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 108df2e3602c..ea40437f246a 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -22,7 +22,7 @@
 #include <linux/tty.h>
 #include <linux/mutex.h>
 #include <linux/magic.h>
-#include <linux/idr.h>
+#include <linux/tida.h>
 #include <linux/devpts_fs.h>
 #include <linux/parser.h>
 #include <linux/fsnotify.h>
@@ -122,7 +122,7 @@ static const match_table_t tokens = {
 };
 
 struct pts_fs_info {
-	struct ida allocated_ptys;
+	struct tida allocated_ptys;
 	struct pts_mount_opts mount_opts;
 	struct super_block *sb;
 	struct dentry *ptmx_dentry;
@@ -377,7 +377,7 @@ static void *new_pts_fs_info(struct super_block *sb)
 	if (!fsi)
 		return NULL;
 
-	ida_init(&fsi->allocated_ptys);
+	tida_init(&fsi->allocated_ptys);
 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 	fsi->sb = sb;
@@ -453,7 +453,7 @@ static void devpts_kill_sb(struct super_block *sb)
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
 
 	if (fsi)
-		ida_destroy(&fsi->allocated_ptys);
+		tida_destroy(&fsi->allocated_ptys);
 	kfree(fsi);
 	kill_litter_super(sb);
 }
@@ -473,29 +473,21 @@ static struct file_system_type devpts_fs_type = {
 int devpts_new_index(struct pts_fs_info *fsi)
 {
 	int index;
-	int ida_ret;
 
-retry:
-	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
-		return -ENOMEM;
+	index = tida_get(&fsi->allocated_ptys, GFP_KERNEL);
+	if (index < 0)
+		return index;
 
 	mutex_lock(&allocated_ptys_lock);
 	if (pty_count >= (pty_limit -
 			  (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
+		tida_put(&fsi->allocated_ptys, index);
 		mutex_unlock(&allocated_ptys_lock);
 		return -ENOSPC;
 	}
 
-	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
-	if (ida_ret < 0) {
-		mutex_unlock(&allocated_ptys_lock);
-		if (ida_ret == -EAGAIN)
-			goto retry;
-		return -EIO;
-	}
-
 	if (index >= fsi->mount_opts.max) {
-		ida_remove(&fsi->allocated_ptys, index);
+		tida_put(&fsi->allocated_ptys, index);
 		mutex_unlock(&allocated_ptys_lock);
 		return -ENOSPC;
 	}
@@ -507,7 +499,7 @@ int devpts_new_index(struct pts_fs_info *fsi)
 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
 {
 	mutex_lock(&allocated_ptys_lock);
-	ida_remove(&fsi->allocated_ptys, idx);
+	tida_put(&fsi->allocated_ptys, idx);
 	pty_count--;
 	mutex_unlock(&allocated_ptys_lock);
 }
-- 
2.1.4