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Subject[PATCH 14/14] tmpfs: no need to use i_lock
2.6.36's 7e496299d4d2 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>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
---
mm/shmem.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
--- linux.orig/mm/shmem.c 2011-05-30 14:25:32.665536626 -0700
+++ linux/mm/shmem.c 2011-05-30 15:03:41.680887254 -0700
@@ -241,9 +241,7 @@ static void shmem_free_blocks(struct ino
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(stru
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);
@@ -1420,9 +1416,7 @@ 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;

@@ -1433,8 +1427,10 @@ 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;
}
@@ -1448,8 +1444,10 @@ 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;
}
@@ -1479,10 +1477,10 @@ 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;

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