XFS_GC_BUF_SIZE
folio_alloc(GFP_KERNEL, get_order(XFS_GC_BUF_SIZE));
data->scratch_size = XFS_GC_BUF_SIZE * XFS_GC_NR_BUFS;
unsigned int this_off = off % XFS_GC_BUF_SIZE;
unsigned int this_len = min(len, XFS_GC_BUF_SIZE - this_off);
data->scratch_folios[off / XFS_GC_BUF_SIZE],
min(howmany(len, XFS_GC_BUF_SIZE) + 1, XFS_GC_NR_BUFS),