On 6.12.18 г. 0:51 ч., Christoph Hellwig wrote:
> XFS currently uses kmalloc for buffers smaller than the page size to
> avoid wasting too much memory. But this can cause a problem with slub
> debugging turned on as the allocations might not be naturally aligned.
> On block devices that require sector size alignment this can lead to
> data corruption.
>
> Give that our smaller than page size buffers are always sector sized
> on a live file system, we can just create a kmem_cache with an
> explicitly specified alignment requirement for this case to fix this
> case without much effort.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>
> Changes since v1:
> - document the decision to use a single cache per file system in
> a comment
> - update the commit log a bit
>
> fs/xfs/xfs_buf.c | 23 +++++++++--------------
> fs/xfs/xfs_mount.h | 2 ++
> fs/xfs/xfs_super.c | 28 ++++++++++++++++++++++++++++
> 3 files changed, 39 insertions(+), 14 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index b21ea2ba768d..904d45f93ce7 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -339,8 +339,10 @@ xfs_buf_free(
>
> __free_page(page);
> }
> - } else if (bp->b_flags & _XBF_KMEM)
> - kmem_free(bp->b_addr);
> + } else if (bp->b_flags & _XBF_KMEM) {
> + kmem_cache_free(bp->b_target->bt_mount->m_sector_cache,
> + bp->b_addr);
> + }
> _xfs_buf_free_pages(bp);
> xfs_buf_free_maps(bp);
> kmem_zone_free(xfs_buf_zone, bp);
> @@ -354,6 +356,7 @@ xfs_buf_allocate_memory(
> xfs_buf_t *bp,
> uint flags)
> {
> + struct xfs_mount *mp = bp->b_target->bt_mount;
> size_t size;
> size_t nbytes, offset;
> gfp_t gfp_mask = xb_to_gfp(flags);
> @@ -362,25 +365,17 @@ xfs_buf_allocate_memory(
> int error;
>
> /*
> - * for buffers that are contained within a single page, just allocate
> - * the memory from the heap - there's no need for the complexity of
> - * page arrays to keep allocation down to order 0.
> + * Use a special slab cache for sector sized buffers when sectors are
> + * small than a page to avoid wasting lots of memory.
nit: s/small/smaller/
<snip>
