[Virtio-fs] [PATCH 1/2] virtio-fs: try hard to do inline reclaim

[Vivek Goyal]

On Tue, Aug 13, 2019 at 02:32:04AM +0800, Liu Bo wrote:
> The difference between inline dmap reclaim and background dmap reclaim is
> that dmaps got from inline reclaim get reused for another mapping
> immediately, according to how we implement REMOVEMAPPING in daemon, it's
> unnecessary to involve a REMOVEMAPPING to reuse a dmap.
> 
> Currently we always kick background reclaim before doing inline reclaim,
> but some lock contention on i_dmap_lock from background reclaim results in
> performance loss for dax read/write.

How much is the performance gain by preferring inline reclaim?

Given how complex dax range reclaim code is becoming, I prefer to
avoid taking anything which comes only with very small gains.

Thanks
Vivek

> 
> This makes read/write first try hard to do inline reclaim, then kick
> background reclaim if it makes no progress.
> 
> Signed-off-by: Liu Bo <bo.liu at linux.alibaba.com>
> ---
>  fs/fuse/file.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index ae197be..2ea670a 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -203,7 +203,8 @@ static void kick_dmap_free_worker(struct fuse_conn *fc, unsigned long delay_ms)
>  	spin_unlock(&fc->lock);
>  }
>  
> -static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
> +static struct fuse_dax_mapping *__alloc_dax_mapping(struct fuse_conn *fc,
> +						    bool bg_reclaim)
>  {
>  	struct fuse_dax_mapping *dmap = NULL;
>  
> @@ -224,9 +225,14 @@ static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
>  	spin_unlock(&fc->lock);
>  
>  out_kick:
> -	kick_dmap_free_worker(fc, 0);
> +	if (bg_reclaim)
> +		kick_dmap_free_worker(fc, 0);
>  	return dmap;
>  }
> +static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
> +{
> +	return __alloc_dax_mapping(fc, true);
> +}
>  
>  /* This assumes fc->lock is held */
>  static void __dmap_remove_busy_list(struct fuse_conn *fc,
> @@ -4085,7 +4091,7 @@ static struct fuse_dax_mapping *alloc_dax_mapping_reclaim(struct fuse_conn *fc,
>  	struct fuse_inode *fi = get_fuse_inode(inode);
>  
>  	while(1) {
> -		dmap = alloc_dax_mapping(fc);
> +		dmap = __alloc_dax_mapping(fc, false);
>  		if (dmap)
>  			return dmap;
>  
> @@ -4099,6 +4105,11 @@ static struct fuse_dax_mapping *alloc_dax_mapping_reclaim(struct fuse_conn *fc,
>  		 * Wait for one.
>  		 */
>  		if (!(fc->nr_free_ranges > 0)) {
> +			/* try again with background reclaim. */
> +			dmap = alloc_dax_mapping(fc);
> +			if (dmap)
> +				return dmap;
> +
>  			if (wait_event_killable_exclusive(fc->dax_range_waitq,
>  					(fc->nr_free_ranges > 0)))
>  				return ERR_PTR(-EINTR);
> -- 
> 1.8.3.1
> 
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