On Wed, Feb 22, 2017 at 02:05:05PM +0000, Filipe Manana wrote:
> On Wed, Feb 22, 2017 at 12:07 AM, Liu Bo <bo.li....@oracle.com> wrote:
> > On Sun, Feb 19, 2017 at 08:56:39PM +0000, fdman...@kernel.org wrote:
> >> From: Filipe Manana <fdman...@suse.com>
> >>
> >> Before attempting to split a leaf we try to migrate items from the leaf to
> >> its right and left siblings. We start by trying to move items into the
> >> rigth sibling and, if the new item is meant to be inserted at the end of
> >> our leaf, we try to free from our leaf an amount of bytes equal to the
> >> number of bytes used by the new item, by setting the variable space_needed
> >> to the byte size of that new item. However if we fail to move enough items
> >> to the right sibling due to lack of space in that sibling, we then try
> >> to move items into the left sibling, and in that case we try to free
> >> an amount equal to the size of the new item from our leaf, when we need
> >> only to free an amount corresponding to the size of the new item minus
> >> the current free space of our leaf. So make sure that before we try to
> >> move items to the left sibling we do set the variable space_needed with
> >> a value corresponding to the new item's size minus the leaf's current
> >> free space.
> >>
> >> Signed-off-by: Filipe Manana <fdman...@suse.com>
> >> ---
> >> fs/btrfs/ctree.c | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >>
> >> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> >> index a426dc8..1d66761 100644
> >> --- a/fs/btrfs/ctree.c
> >> +++ b/fs/btrfs/ctree.c
> >> @@ -4160,6 +4160,9 @@ static noinline int push_for_double_split(struct
> >> btrfs_trans_handle *trans,
> >>
> >> /* try to push all the items before our slot into the next leaf */
> >> slot = path->slots[0];
> >> + space_needed = data_size;
> >> + if (slot > 0)
> >> + space_needed -= btrfs_leaf_free_space(fs_info,
> >> path->nodes[0]);
> >
> > Good point.
> >
> >> ret = push_leaf_left(trans, root, path, 1, space_needed, 0, slot);
> >> if (ret < 0)
> >> return ret;
> >> @@ -4215,6 +4218,10 @@ static noinline int split_leaf(struct
> >> btrfs_trans_handle *trans,
> >> if (wret < 0)
> >> return wret;
> >> if (wret) {
> >> + space_needed = data_size;
> >> + if (slot > 0)
> >> + space_needed -=
> >> btrfs_leaf_free_space(fs_info,
> >> + l);
> >
> > Not sure if we need this, the above push_leaf_right() was called with
> > @min_data_size == space_needed, thus if @wret == 1, no items have been
> > moved in
> > push_leaf_right() so that leaf 'l' remains unchanged.
>
> That's exactly the point. If the item is meant to be appended and we
> failed to move it into the right sibling, we want to try to move items
> from the leaf into its left sibling with the goal of freeing
> "new_item_size - leaf_free_space(l)" bytes from our leaf. Without this
> new assignment, we try to free new_item_size bytes, which has higher
> chances of not being successful at migrating items into the left
> sibling (example, the left sibling has less than new_item_size bytes
> free, but has at least "new_item_size - leaf_free_space(l)" bytes
> free).
>
I see, I missed that we didn't check (slot > 0) before
push_leaf_right(), you may add
Reviewed-by: Liu Bo <bo.li....@oracle.com>
Thanks,
-liubo
> >
> > Thanks,
> >
> > -liubo
> >> wret = push_leaf_left(trans, root, path,
> >> space_needed,
> >> space_needed, 0, (u32)-1);
> >> if (wret < 0)
> >> --
> >> 2.7.0.rc3
> >>
> >> --
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