Hello Jan,
> 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.
Anyway, your original code looks messy about passing arg gfp_t..isn't it?
And you pass GFP_NOFS to a function, but in fact this function is surrounded
by rw locks.
I make it clear to the caller what kind of gfp_t we should pass(although now we always
come to GFP_ATOMIC)...
>
> -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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