[0/3] btrfs: trim latency improvements
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Message ID 20180906211816.12121-1-jeffm@suse.com
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  • btrfs: trim latency improvements
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Jeff Mahoney Sept. 6, 2018, 9:18 p.m. UTC
From: Jeff Mahoney <jeffm@suse.com>

This patch set fixes a few issues with trim.

1) Fix device list iteration.  We're iterating the ->alloc_list while
   holding the device_list_mutex.  The ->alloc_list is protected by
   the chunk mutex and we don't want to hold it across the entire
   trim execution.  Instead, use the ->devices list, which is protected
   by the device_list_mutex.

2) Skip trim on devices that don't support it.  Rather than letting
   the block layer reject it, bounce out early.

3) Don't keep the commit_root_sem locked and the transaction pinned
   across the block layer component of trim.  We only need these to
   ensure the pending chunks list doesn't go away underneath us, so
   it's safe to drop across the trim itself.  Historically, this
   caused issues when fstrim and balance would run at the same time
   since balance would produce lots of transactions and would
   have to wait constantly, causing problems for everything else that
   wanted to start a transaction.

-Jeff
---

Jeff Mahoney (3):
  btrfs: use ->devices list instead of ->alloc_list in btrfs_trim_fs
  btrfs: don't attempt to trim devices that don't support it
  btrfs: keep trim from interfering with transaction commits

 fs/btrfs/extent-tree.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

Comments

David Sterba Sept. 14, 2018, 4:33 p.m. UTC | #1
On Thu, Sep 06, 2018 at 05:18:13PM -0400, jeffm@suse.com wrote:
> From: Jeff Mahoney <jeffm@suse.com>
> 
> This patch set fixes a few issues with trim.
> 
> 1) Fix device list iteration.  We're iterating the ->alloc_list while
>    holding the device_list_mutex.  The ->alloc_list is protected by
>    the chunk mutex and we don't want to hold it across the entire
>    trim execution.  Instead, use the ->devices list, which is protected
>    by the device_list_mutex.
> 
> 2) Skip trim on devices that don't support it.  Rather than letting
>    the block layer reject it, bounce out early.
> 
> 3) Don't keep the commit_root_sem locked and the transaction pinned
>    across the block layer component of trim.  We only need these to
>    ensure the pending chunks list doesn't go away underneath us, so
>    it's safe to drop across the trim itself.  Historically, this
>    caused issues when fstrim and balance would run at the same time
>    since balance would produce lots of transactions and would
>    have to wait constantly, causing problems for everything else that
>    wanted to start a transaction.
> 
> -Jeff
> ---
> 
> Jeff Mahoney (3):
>   btrfs: use ->devices list instead of ->alloc_list in btrfs_trim_fs
>   btrfs: don't attempt to trim devices that don't support it
>   btrfs: keep trim from interfering with transaction commits

The patches have been in for-next for some time, I'm moving them to
misc-next now and will probably forward them to the next rc (5) with
other trim fixes from Qu.

Please note that the commit subject in the Fixes: tag should be in
"...", I've fixed that.