On Tue, May 07, 2013 at 08:20 (+0200), Wang Shilong wrote:
> If you look the code carefully, you will see all the tree_mod_alloc()
> has to use GFP_ATOMIC. However, the original code pass the wrong arg
> gfp_t in some places, this dosen't cause any problems, because in the
> tree_mod_alloc(), it ignores arg gfp_t and just use GFP_ATOMIC directly,
> this is not good.
>
> However, i think we should try best not to allocate with GFP_ATOMIC, so
> i keep the gfp_t there in the hope we can change allocation mode in the
> future.
NAK.
The code as it is now is prepared to get rid of at least some GFP_ATOMIC
allocations. You won't get rid of all of them, as there are a lot of spin lock
situations where we need to add to the tree mod lock anyway.
As a preparation we currently pass the "best" flags (least restrictive) we can
instead of always passing GFP_ATOMIC. I pointed you to this comment already:
557 /*
558 * once we switch from spin locks to something different, we should
559 * honor the flags parameter here.
560 */
561 tm = *tm_ret = kzalloc(sizeof(*tm), GFP_ATOMIC);
So, if you want less atomic allocations, find something more suitable than an
rwlock for fs_info->tree_mod_log_lock an you can in fact replace "GFP_ATOMIC"
with "flags" in the kzalloc().
The good thing is, because everything is already prepared you don't have to
think about all the callers again an pass the correct flags.
-Jan
> Signed-off-by: Wang Shilong <wangsl-fnst@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/ctree.c | 37 ++++++++++++++++++-------------------
> 1 files changed, 18 insertions(+), 19 deletions(-)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index de6de8e..33c9061 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -553,7 +553,7 @@ static inline int tree_mod_alloc(struct btrfs_fs_info *fs_info, gfp_t flags,
> * once we switch from spin locks to something different, we should
> * honor the flags parameter here.
> */
> - tm = *tm_ret = kzalloc(sizeof(*tm), GFP_ATOMIC);
> + tm = *tm_ret = kzalloc(sizeof(*tm), flags);
> if (!tm)
> return -ENOMEM;
>
> @@ -591,14 +591,14 @@ __tree_mod_log_insert_key(struct btrfs_fs_info *fs_info,
> static noinline int
> tree_mod_log_insert_key_mask(struct btrfs_fs_info *fs_info,
> struct extent_buffer *eb, int slot,
> - enum mod_log_op op, gfp_t flags)
> + enum mod_log_op op)
> {
> int ret;
>
> if (tree_mod_dont_log(fs_info, eb))
> return 0;
>
> - ret = __tree_mod_log_insert_key(fs_info, eb, slot, op, flags);
> + ret = __tree_mod_log_insert_key(fs_info, eb, slot, op, GFP_ATOMIC);
>
> tree_mod_log_write_unlock(fs_info);
> return ret;
> @@ -608,7 +608,7 @@ static noinline int
> tree_mod_log_insert_key(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
> int slot, enum mod_log_op op)
> {
> - return tree_mod_log_insert_key_mask(fs_info, eb, slot, op, GFP_NOFS);
> + return tree_mod_log_insert_key_mask(fs_info, eb, slot, op);
> }
>
> static noinline int
> @@ -616,13 +616,13 @@ tree_mod_log_insert_key_locked(struct btrfs_fs_info *fs_info,
> struct extent_buffer *eb, int slot,
> enum mod_log_op op)
> {
> - return __tree_mod_log_insert_key(fs_info, eb, slot, op, GFP_NOFS);
> + return __tree_mod_log_insert_key(fs_info, eb, slot, op, GFP_ATOMIC);
> }
>
> static noinline int
> tree_mod_log_insert_move(struct btrfs_fs_info *fs_info,
> struct extent_buffer *eb, int dst_slot, int src_slot,
> - int nr_items, gfp_t flags)
> + int nr_items)
> {
> struct tree_mod_elem *tm;
> int ret;
> @@ -642,7 +642,7 @@ tree_mod_log_insert_move(struct btrfs_fs_info *fs_info,
> BUG_ON(ret < 0);
> }
>
> - ret = tree_mod_alloc(fs_info, flags, &tm);
> + ret = tree_mod_alloc(fs_info, GFP_ATOMIC, &tm);
> if (ret < 0)
> goto out;
>
> @@ -679,7 +679,7 @@ __tree_mod_log_free_eb(struct btrfs_fs_info *fs_info, struct extent_buffer *eb)
> static noinline int
> tree_mod_log_insert_root(struct btrfs_fs_info *fs_info,
> struct extent_buffer *old_root,
> - struct extent_buffer *new_root, gfp_t flags,
> + struct extent_buffer *new_root,
> int log_removal)
> {
> struct tree_mod_elem *tm;
> @@ -691,7 +691,7 @@ tree_mod_log_insert_root(struct btrfs_fs_info *fs_info,
> if (log_removal)
> __tree_mod_log_free_eb(fs_info, old_root);
>
> - ret = tree_mod_alloc(fs_info, flags, &tm);
> + ret = tree_mod_alloc(fs_info, GFP_ATOMIC, &tm);
> if (ret < 0)
> goto out;
>
> @@ -809,19 +809,18 @@ tree_mod_log_eb_move(struct btrfs_fs_info *fs_info, struct extent_buffer *dst,
> {
> int ret;
> ret = tree_mod_log_insert_move(fs_info, dst, dst_offset, src_offset,
> - nr_items, GFP_NOFS);
> + nr_items);
> BUG_ON(ret < 0);
> }
>
> static noinline void
> tree_mod_log_set_node_key(struct btrfs_fs_info *fs_info,
> - struct extent_buffer *eb, int slot, int atomic)
> + struct extent_buffer *eb, int slot)
> {
> int ret;
>
> ret = tree_mod_log_insert_key_mask(fs_info, eb, slot,
> - MOD_LOG_KEY_REPLACE,
> - atomic ? GFP_ATOMIC : GFP_NOFS);
> + MOD_LOG_KEY_REPLACE);
> BUG_ON(ret < 0);
> }
>
> @@ -843,7 +842,7 @@ tree_mod_log_set_root_pointer(struct btrfs_root *root,
> {
> int ret;
> ret = tree_mod_log_insert_root(root->fs_info, root->node,
> - new_root_node, GFP_NOFS, log_removal);
> + new_root_node, log_removal);
> BUG_ON(ret < 0);
> }
>
> @@ -1886,7 +1885,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
> struct btrfs_disk_key right_key;
> btrfs_node_key(right, &right_key, 0);
> tree_mod_log_set_node_key(root->fs_info, parent,
> - pslot + 1, 0);
> + pslot + 1);
> btrfs_set_node_key(parent, &right_key, pslot + 1);
> btrfs_mark_buffer_dirty(parent);
> }
> @@ -1931,7 +1930,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
> struct btrfs_disk_key mid_key;
> btrfs_node_key(mid, &mid_key, 0);
> tree_mod_log_set_node_key(root->fs_info, parent,
> - pslot, 0);
> + pslot);
> btrfs_set_node_key(parent, &mid_key, pslot);
> btrfs_mark_buffer_dirty(parent);
> }
> @@ -2030,7 +2029,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
> orig_slot += left_nr;
> btrfs_node_key(mid, &disk_key, 0);
> tree_mod_log_set_node_key(root->fs_info, parent,
> - pslot, 0);
> + pslot);
> btrfs_set_node_key(parent, &disk_key, pslot);
> btrfs_mark_buffer_dirty(parent);
> if (btrfs_header_nritems(left) > orig_slot) {
> @@ -2083,7 +2082,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>
> btrfs_node_key(right, &disk_key, 0);
> tree_mod_log_set_node_key(root->fs_info, parent,
> - pslot + 1, 0);
> + pslot + 1);
> btrfs_set_node_key(parent, &disk_key, pslot + 1);
> btrfs_mark_buffer_dirty(parent);
>
> @@ -2963,7 +2962,7 @@ static void fixup_low_keys(struct btrfs_root *root, struct btrfs_path *path,
> if (!path->nodes[i])
> break;
> t = path->nodes[i];
> - tree_mod_log_set_node_key(root->fs_info, t, tslot, 1);
> + tree_mod_log_set_node_key(root->fs_info, t, tslot);
> btrfs_set_node_key(t, key, tslot);
> btrfs_mark_buffer_dirty(path->nodes[i]);
> if (tslot != 0)
>
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