Re: [PATCH] btrfs: allow changing 'thread_pool' size at remount time

[Josef Bacik <josef@redhat.com>]

On Tue, Apr 24, 2012 at 08:26:44PM +0300, Sergei Trofimovich wrote:
> From: Sergei Trofimovich <slyfox@gentoo.org>
> 
> Changing 'mount -oremount,thread_pool=2 /' didn't make any effect:
> 
> maximum amount of worker threads is specified in 2 places:
> - in 'strict btrfs_fs_info::thread_pool_size'
> - in each worker struct: 'struct btrfs_workers::max_workers'
> 
> 'mount -oremount' updated only 'btrfs_fs_info::thread_pool_size'.
> 
> Fix it by pushing new maximum value to all created worker structures
> as well.
> 
> Cc: Josef Bacik <josef@redhat.com>
> Cc: Chris Mason <chris.mason@oracle.com>
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> ---
> WARNING: This patch makes sense only with
> WARNING:    "btrfs: fix early abort in 'remount'"
> WARNING: sitting in Josef's -next branch.
>  fs/btrfs/super.c |   38 +++++++++++++++++++++++++++++++++-----
>  1 files changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 2f28fc0..ed2dab9 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -435,11 +435,8 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
>  		case Opt_thread_pool:
>  			intarg = 0;
>  			match_int(&args[0], &intarg);
> -			if (intarg) {
> +			if (intarg)
>  				info->thread_pool_size = intarg;
> -				printk(KERN_INFO "btrfs: thread pool %d\n",
> -				       info->thread_pool_size);
> -			}
>  			break;
>  		case Opt_max_inline:
>  			num = match_strdup(&args[0]);
> @@ -1119,6 +1116,35 @@ error_fs_info:
>  	return ERR_PTR(error);
>  }
>  
> +static void btrfs_set_max_workers(struct btrfs_workers *workers, int new_limit)
> +{
> +	workers->max_workers = new_limit;
> +}

This needs to be protected by it's spin lock, so do

spin_lock_irq(&workers->lock);
workers->max_workers = new_limit;
spin_unlock_irq(&workers->lock);

Also this doesn't do anything for thread pools that have already gone above the
new maximum.  In practice this shouldn't happen really since most of these
workers are related to writing anyway, but it may be prudent in the future to
make btrfs_set_max_workers to go through and stop threads until the workers are
below the new limit.  This doesn't have to be done in this patch, just good idea
for future work.

> +
> +static void btrfs_resize_thread_pool(struct btrfs_fs_info *fs_info, int new_pool_size, int old_pool_size)
> +{
> +	if (new_pool_size != old_pool_size) {
> +		fs_info->thread_pool_size = new_pool_size;
> +
> +		printk(KERN_INFO "btrfs: resize thread pool %d -> %d\n", old_pool_size, new_pool_size);
> +
> +		btrfs_set_max_workers(&fs_info->generic_worker, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->delalloc_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->submit_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->caching_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->fixup_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->endio_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->endio_meta_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->endio_meta_write_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->endio_write_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->endio_freespace_worker, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->delayed_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->readahead_workers, new_pool_size);
> +		btrfs_set_max_workers(&fs_info->scrub_workers, new_pool_size);
> +	}
> +}
> +

These lines are past the 80 column mark, if you are using vim do

:set textwidth=80

and that should help.  Thanks,

Josef