Re: [PATCH 2/2] xfs: fix deadlock and streamline xfs_getfsmap performance

Christoph Hellwig
2020-10-06T06:26:28Z

On Mon, Oct 05, 2020 at 11:21:36AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> Refactor xfs_getfsmap to improve its performance: instead of indirectly
> calling a function that copies one record to userspace at a time, create
> a shadow buffer in the kernel and copy the whole array once at the end.
> On the author's computer, this reduces the runtime on his /home by ~20%.
>
> This also eliminates a deadlock when running GETFSMAP against the
> realtime device. The current code locks the rtbitmap to create
> fsmappings and copies them into userspace, having not released the
> rtbitmap lock. If the userspace buffer is an mmap of a sparse file that
> itself resides on the realtime device, the write page fault will recurse
> into the fs for allocation, which will deadlock on the rtbitmap lock.
>
> Fixes: 4c934c7dd60c ("xfs: report realtime space information via the rtbitmap")
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>