Re: [PATCH 04/28] xfs: Improve metadata buffer reclaim accountability

[Darrick J. Wong]

On Fri, Nov 01, 2019 at 10:45:54AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> The buffer cache shrinker frees more than just the xfs_buf slab
> objects - it also frees the pages attached to the buffers. Make sure
> the memory reclaim code accounts for this memory being freed
> correctly, similar to how the inode shrinker accounts for pages
> freed from the page cache due to mapping invalidation.
> 
> We also need to make sure that the mm subsystem knows these are
> reclaimable objects. We provide the memory reclaim subsystem with a
> a shrinker to reclaim xfs_bufs, so we should really mark the slab
> that way.
> 
> We also have a lot of xfs_bufs in a busy system, spread them around
> like we do inodes.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_buf.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 1e63dd3d1257..d34e5d2edacd 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -324,6 +324,9 @@ xfs_buf_free(
>  
>  			__free_page(page);
>  		}
> +		if (current->reclaim_state)
> +			current->reclaim_state->reclaimed_slab +=
> +							bp->b_page_count;
>  	} else if (bp->b_flags & _XBF_KMEM)
>  		kmem_free(bp->b_addr);
>  	_xfs_buf_free_pages(bp);
> @@ -2061,7 +2064,8 @@ int __init
>  xfs_buf_init(void)
>  {
>  	xfs_buf_zone = kmem_zone_init_flags(sizeof(xfs_buf_t), "xfs_buf",
> -						KM_ZONE_HWALIGN, NULL);
> +			KM_ZONE_HWALIGN | KM_ZONE_SPREAD | KM_ZONE_RECLAIM,

As discussed on the previous iteration of this series, I'd like to
capture the reasons for adding KM_ZONE_SPREAD as a separate patch.

--D

> +			NULL);
>  	if (!xfs_buf_zone)
>  		goto out;
>  
> -- 
> 2.24.0.rc0
>