On Wed, Jul 02, 2014 at 10:28:17AM +0800, Miao Xie wrote:
> On Tue, 1 Jul 2014 17:28:46 +0800, Liu Bo wrote:
> > This percpu counter @total_bytes_pinned is introduced to skip unnecessary
> > operations of 'commit transaction', it accounts for those space we may free
> > but are stuck in delayed refs.
> >
> > And we zero out @space_info->total_bytes_pinned every transaction period so
> > we have a better idea of how much space we'll actually free up by committing
> > this transaction. However, we do the 'zero out' part a little earlier,
> > before
> > we actually unpin space, so we end up returning ENOSPC when we actually have
> > free space that's just unpinned from committing transaction.
> >
> > xfstests/generic/074 complained then.
> >
> > This fixes it by actually accounting the percpu pinned number when 'unpin',
> > and when finding space for writing, if it finds that pinned bytes is less
> > than needed, we first try again to check if we have space now, as someone
> > may have committed transaction, yes means we're good, while no means we
> > really have run out of space.
> >
> > Signed-off-by: Liu Bo <[email protected]>
> > ---
> > v3: Really account the percpu pinned number when unpin, instead of zeroing
> > it out, as we set transaction with UNBLOCKED before 'unpin', zeroing it
> > out may end up with messing percpu pinned number(suggested by Miao).
> > v2: Add missing brakets for if statement
> >
> > fs/btrfs/extent-tree.c | 20 ++++++++++++--------
> > 1 file changed, 12 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> > index 99c2539..f36fb13 100644
> > --- a/fs/btrfs/extent-tree.c
> > +++ b/fs/btrfs/extent-tree.c
> > @@ -3685,7 +3685,7 @@ int btrfs_check_data_free_space(struct inode *inode,
> > u64 bytes)
> > struct btrfs_root *root = BTRFS_I(inode)->root;
> > struct btrfs_fs_info *fs_info = root->fs_info;
> > u64 used;
> > - int ret = 0, committed = 0, alloc_chunk = 1;
> > + int ret = 0, committed = 0, alloc_chunk = 1, check_pinned = 0;
> >
> > /* make sure bytes are sectorsize aligned */
> > bytes = ALIGN(bytes, root->sectorsize);
> > @@ -3756,11 +3756,18 @@ alloc:
> > * allocation don't bother committing the transaction.
> > */
> > if (percpu_counter_compare(&data_sinfo->total_bytes_pinned,
> > - bytes) < 0)
> > - committed = 1;
> > + bytes) < 0) {
> > + if (check_pinned) {
> > + committed = 1; /* really run out of space. */
> > + } else {
> > + check_pinned = 1;
> > + spin_unlock(&data_sinfo->lock);
> > + goto again;
> > + }
> > + }
>
> Is there anything wrong in the original code? I think we needn't change the
> code here
> because we are not sure anyone would commit the transaction, and though
> someone is
> committing the transaction, the process is slow, we still need commit the
> transaction
> by ourselves mostly(In fact, this commit is just to wait the transaction to
> complete)
> (The above analysis has not been confirmed)
oops, I agree that they're no more needed.
I made these changes based on zeroing pinned number in
btrfs_prepare_extent_commit(), if someone has committed the transaction and
been running btrfs_prepare_extent_commit(), the pinned number is here 0 byte
but we'll own free space as soon as finishing btrfs_finish_extent_commit()
later, so I made it 'goto again' to see if we can skip committing transaction.
However, we don't need it any more, now pinned number is calculated within
@sinfo->lock in unpin_extent_range(), (its value < bytes) means we have no
enough space for this write.
-liubo
>
> Thanks
> Miao
>
> > spin_unlock(&data_sinfo->lock);
> >
> > - /* commit the current transaction and try again */
> > + /* commit the current transaction and try again */
> > commit_trans:
> > if (!committed &&
> > !atomic_read(&root->fs_info->open_ioctl_trans)) {
> > @@ -5678,7 +5685,6 @@ void btrfs_prepare_extent_commit(struct
> > btrfs_trans_handle *trans,
> > struct btrfs_caching_control *next;
> > struct btrfs_caching_control *caching_ctl;
> > struct btrfs_block_group_cache *cache;
> > - struct btrfs_space_info *space_info;
> >
> > down_write(&fs_info->commit_root_sem);
> >
> > @@ -5701,9 +5707,6 @@ void btrfs_prepare_extent_commit(struct
> > btrfs_trans_handle *trans,
> >
> > up_write(&fs_info->commit_root_sem);
> >
> > - list_for_each_entry_rcu(space_info, &fs_info->space_info, list)
> > - percpu_counter_set(&space_info->total_bytes_pinned, 0);
> > -
> > update_global_block_rsv(fs_info);
> > }
> >
> > @@ -5741,6 +5744,7 @@ static int unpin_extent_range(struct btrfs_root
> > *root, u64 start, u64 end)
> > spin_lock(&cache->lock);
> > cache->pinned -= len;
> > space_info->bytes_pinned -= len;
> > + percpu_counter_add(&space_info->total_bytes_pinned, -len);
> > if (cache->ro) {
> > space_info->bytes_readonly += len;
> > readonly = true;
> >
>
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
