tmpfs: no need to use i_lock
Hugh Dickins [Tue, 26 Jul 2011 00:12:26 +0000 (17:12 -0700)]
2.6.36's 7e496299d4d2 ("tmpfs: make tmpfs scalable with percpu_counter for
used blocks") to make tmpfs scalable with percpu_counter used
inode->i_lock in place of sbinfo->stat_lock around i_blocks updates; but
that was adverse to scalability, and unnecessary, since info->lock is
already held there in the fast paths.

Remove those uses of i_lock, and add info->lock in the three error paths
where it's then needed across shmem_free_blocks().  It's not actually
needed across shmem_unacct_blocks(), but they're so often paired that it
looks wrong to split them apart.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shmem.c

index fcedf54..c1db11c 100644 (file)
@@ -241,9 +241,7 @@ static void shmem_free_blocks(struct inode *inode, long pages)
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        if (sbinfo->max_blocks) {
                percpu_counter_add(&sbinfo->used_blocks, -pages);
-               spin_lock(&inode->i_lock);
                inode->i_blocks -= pages*BLOCKS_PER_PAGE;
-               spin_unlock(&inode->i_lock);
        }
 }
 
@@ -432,9 +430,7 @@ static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long
                                                sbinfo->max_blocks - 1) >= 0)
                                return ERR_PTR(-ENOSPC);
                        percpu_counter_inc(&sbinfo->used_blocks);
-                       spin_lock(&inode->i_lock);
                        inode->i_blocks += BLOCKS_PER_PAGE;
-                       spin_unlock(&inode->i_lock);
                }
 
                spin_unlock(&info->lock);
@@ -1421,9 +1417,7 @@ repeat:
                            shmem_acct_block(info->flags))
                                goto nospace;
                        percpu_counter_inc(&sbinfo->used_blocks);
-                       spin_lock(&inode->i_lock);
                        inode->i_blocks += BLOCKS_PER_PAGE;
-                       spin_unlock(&inode->i_lock);
                } else if (shmem_acct_block(info->flags))
                        goto nospace;
 
@@ -1434,8 +1428,10 @@ repeat:
                                spin_unlock(&info->lock);
                                filepage = shmem_alloc_page(gfp, info, idx);
                                if (!filepage) {
+                                       spin_lock(&info->lock);
                                        shmem_unacct_blocks(info->flags, 1);
                                        shmem_free_blocks(inode, 1);
+                                       spin_unlock(&info->lock);
                                        error = -ENOMEM;
                                        goto failed;
                                }
@@ -1449,8 +1445,10 @@ repeat:
                                        current->mm, GFP_KERNEL);
                                if (error) {
                                        page_cache_release(filepage);
+                                       spin_lock(&info->lock);
                                        shmem_unacct_blocks(info->flags, 1);
                                        shmem_free_blocks(inode, 1);
+                                       spin_unlock(&info->lock);
                                        filepage = NULL;
                                        goto failed;
                                }
@@ -1480,10 +1478,10 @@ repeat:
                         * be done automatically.
                         */
                        if (ret) {
-                               spin_unlock(&info->lock);
-                               page_cache_release(filepage);
                                shmem_unacct_blocks(info->flags, 1);
                                shmem_free_blocks(inode, 1);
+                               spin_unlock(&info->lock);
+                               page_cache_release(filepage);
                                filepage = NULL;
                                if (error)
                                        goto failed;