On Wed, Dec 12, 2018 at 06:01:57PM +0200, Nikolay Borisov wrote:
>
>
> On 3.12.18 г. 17:24 ч., Josef Bacik wrote:
> > With severe fragmentation we can end up with our inode rsv size being
> > huge during writeout, which would cause us to need to make very large
> > metadata reservations. However we may not actually need that much once
>
> The sentence beginning with "However" needs more information, why might
> we not need that much once writeout is complete?
Updated in changelog
> > writeout is complete. So instead try to make our reservation, and if we
> > couldn't make it re-calculate our new reservation size and try again.
>
> Why do you think that recalculating the requested bytes will be
> different the 2nd time ?
Partly answered in the comment in the code
>
> > If our reservation size doesn't change between tries then we know we are
> > actually out of space and can error out.
> >
> > Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> > ---
> > fs/btrfs/extent-tree.c | 58 +++++++++++++++++++++++++++++++++++++-------------
> > 1 file changed, 43 insertions(+), 15 deletions(-)
> >
> > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> > index 0ee77a98f867..0e1a499035ac 100644
> > --- a/fs/btrfs/extent-tree.c
> > +++ b/fs/btrfs/extent-tree.c
> > @@ -5787,6 +5787,21 @@ int btrfs_block_rsv_refill(struct btrfs_root *root,
> > return ret;
> > }
> >
> > +static inline void __get_refill_bytes(struct btrfs_block_rsv *block_rsv,
> > + u64 *metadata_bytes, u64 *qgroup_bytes)
>
> This function needs a better name. Something like calc_required_bytes or
> calc_refill_bytes
renamed to calc_refill_bytes
>
> > +{
> > + *metadata_bytes = 0;
> > + *qgroup_bytes = 0;
> > +
> > + spin_lock(&block_rsv->lock);
> > + if (block_rsv->reserved < block_rsv->size)
> > + *metadata_bytes = block_rsv->size - block_rsv->reserved;
> > + if (block_rsv->qgroup_rsv_reserved < block_rsv->qgroup_rsv_size)
> > + *qgroup_bytes = block_rsv->qgroup_rsv_size -
> > + block_rsv->qgroup_rsv_reserved;
> > + spin_unlock(&block_rsv->lock);
> > +}
> > +
> > /**
> > * btrfs_inode_rsv_refill - refill the inode block rsv.
> > * @inode - the inode we are refilling.
> > @@ -5802,25 +5817,39 @@ static int btrfs_inode_rsv_refill(struct btrfs_inode *inode,
> > {
> > struct btrfs_root *root = inode->root;
> > struct btrfs_block_rsv *block_rsv = &inode->block_rsv;
> > - u64 num_bytes = 0;
> > + u64 num_bytes = 0, last = 0;
> > u64 qgroup_num_bytes = 0;
> > int ret = -ENOSPC;
> >
> > - spin_lock(&block_rsv->lock);
> > - if (block_rsv->reserved < block_rsv->size)
> > - num_bytes = block_rsv->size - block_rsv->reserved;
> > - if (block_rsv->qgroup_rsv_reserved < block_rsv->qgroup_rsv_size)
> > - qgroup_num_bytes = block_rsv->qgroup_rsv_size -
> > - block_rsv->qgroup_rsv_reserved;
> > - spin_unlock(&block_rsv->lock);
> > -
> > + __get_refill_bytes(block_rsv, &num_bytes, &qgroup_num_bytes);
> > if (num_bytes == 0)
> > return 0;
> >
> > - ret = btrfs_qgroup_reserve_meta_prealloc(root, qgroup_num_bytes, true);
> > - if (ret)
> > - return ret;
> > - ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
> > + do {
> > + ret = btrfs_qgroup_reserve_meta_prealloc(root, qgroup_num_bytes, true);
> > + if (ret)
> > + return ret;
> > + ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
> > + if (ret) {
> > + btrfs_qgroup_free_meta_prealloc(root, qgroup_num_bytes);
> > + last = num_bytes;
> > + /*
> > + * If we are fragmented we can end up with a lot of
> > + * outstanding extents which will make our size be much
> > + * larger than our reserved amount. If we happen to
> > + * try to do a reservation here that may result in us
> > + * trying to do a pretty hefty reservation, which we may
> > + * not need once delalloc flushing happens. If this is
>
> The "If we happen" sentence needs to be reworded because it's -ENOPARSE.
> Perhaps one of the "to do a reservation" should go away?
Reworded
