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

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH v4 8/8] xfs: add background scanning to clear EOFBLOCKS inodes
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 28 Sep 2012 18:00:09 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1348767952-24229-9-git-send-email-bfoster@xxxxxxxxxx>
References: <1348767952-24229-1-git-send-email-bfoster@xxxxxxxxxx> <1348767952-24229-9-git-send-email-bfoster@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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@xxxxxxxxxx>
> ---
>  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....

>  
>  #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...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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