Re: [PATCH v4 8/8] xfs: add background scanning to clear EOFBLOCKS inodes

[Brian Foster <bfoster@redhat.com>]

On 09/28/2012 04:00 AM, Dave Chinner wrote:
> On Thu, Sep 27, 2012 at 01:45:52PM -0400, Brian Foster wrote:
>> Create a delayed_work to enable background scanning and freeing
>> of EOFBLOCKS inodes. The scanner kicks in once speculative
>> preallocation occurs and stops requeueing itself when no EOFBLOCKS
>> inodes exist.
>>
>> Scans are queued on the existing syncd workqueue and the interval
>> is based on the new eofb_timer tunable (default to 5m). The
>> background scanner performs unfiltered, best effort scans (which
>> skips inodes under lock contention or with a dirty cache mapping).
>>
>> Signed-off-by: Brian Foster <bfoster@redhat.com>
>> ---
>>  fs/xfs/xfs_globals.c |    1 +
>>  fs/xfs/xfs_linux.h   |    1 +
>>  fs/xfs/xfs_mount.h   |    2 ++
>>  fs/xfs/xfs_sync.c    |   30 ++++++++++++++++++++++++++++++
>>  fs/xfs/xfs_sysctl.c  |    9 +++++++++
>>  fs/xfs/xfs_sysctl.h  |    1 +
>>  6 files changed, 44 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_globals.c b/fs/xfs/xfs_globals.c
>> index 76e81cf..fda9a66 100644
>> --- a/fs/xfs/xfs_globals.c
>> +++ b/fs/xfs/xfs_globals.c
>> @@ -40,4 +40,5 @@ xfs_param_t xfs_params = {
>>  	.rotorstep	= {	1,		1,		255	},
>>  	.inherit_nodfrg	= {	0,		1,		1	},
>>  	.fstrm_timer	= {	1,		30*100,		3600*100},
>> +	.eofb_timer	= {	1*100,		300*100,	7200*100},
>>  };
>> diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
>> index 828662f..bbad99b 100644
>> --- a/fs/xfs/xfs_linux.h
>> +++ b/fs/xfs/xfs_linux.h
>> @@ -118,6 +118,7 @@
>>  #define xfs_rotorstep		xfs_params.rotorstep.val
>>  #define xfs_inherit_nodefrag	xfs_params.inherit_nodfrg.val
>>  #define xfs_fstrm_centisecs	xfs_params.fstrm_timer.val
>> +#define xfs_eofb_centisecs	xfs_params.eofb_timer.val
> 
> Let's not propagate that stupid "centiseconds" unit any further.
> Nobody uses it, and it was only introduced because jiffie was 10ms
> and there were 100 to a second so it was easy to convert in the
> code. I don't think there is any reason for needing sub-second
> granularity for this background function, so seconds shoul dbe just
> fine for it. If you think we nee dfiner granularity, milliseconds is
> the nex tunit to choose....
> 

I think seconds is fine. I chose 1s for a minimum, but even that is
pathological and really only useful for focused stress testing.

>>  
>>  #define current_cpu()		(raw_smp_processor_id())
>>  #define current_pid()		(current->pid)
>> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
>> index deee09e..bf5ecfa 100644
>> --- a/fs/xfs/xfs_mount.h
>> +++ b/fs/xfs/xfs_mount.h
>> @@ -199,6 +199,8 @@ typedef struct xfs_mount {
>>  	struct xfs_mru_cache	*m_filestream;  /* per-mount filestream data */
>>  	struct delayed_work	m_sync_work;	/* background sync work */
>>  	struct delayed_work	m_reclaim_work;	/* background inode reclaim */
>> +	struct delayed_work	m_eofblocks_work; /* background eof blocks
>> +						     trimming */
>>  	struct work_struct	m_flush_work;	/* background inode flush */
>>  	__int64_t		m_update_flags;	/* sb flags we need to update
>>  						   on the next remount,rw */
>> diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
>> index c9e1c16..31f678a 100644
>> --- a/fs/xfs/xfs_sync.c
>> +++ b/fs/xfs/xfs_sync.c
>> @@ -532,6 +532,31 @@ xfs_flush_worker(
>>  	xfs_sync_data(mp, SYNC_TRYLOCK | SYNC_WAIT);
>>  }
>>  
>> +/*
>> + * Background scanning to trim post-EOF preallocated space. This is queued
>> + * based on the 'eofb_centisecs' tunable (5m by default).
>> + */
>> +STATIC void
>> +xfs_queue_eofblocks(
>> +	struct xfs_mount *mp)
>> +{
>> +	rcu_read_lock();
>> +	if (radix_tree_tagged(&mp->m_perag_tree, XFS_ICI_EOFBLOCKS_TAG))
>> +		queue_delayed_work(xfs_syncd_wq, &mp->m_eofblocks_work,
>> +			msecs_to_jiffies(xfs_eofb_centisecs * 10));
>> +	rcu_read_unlock();
>> +}
> 
> This will all need reworking for the new xfs_icache.c and per-mount
> workqueue structuring. Fundamentally there is nothing wrong with
> what you've done, it's just been reworked...
> 
>> +	{
>> +		.procname	= "eofb_centisecs",
> 
> Ugh. Call it something users might understand. Say
> "background_prealloc_discard_period", or something similarly
> informative...
> 

Ok. Thanks for the review.

Brian

> Cheers,
> 
> Dave.
> 

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