MRG_CTX_HEADER_SHIFT
return (void *)(unsigned long)((headroom << MRG_CTX_HEADER_SHIFT) | truesize);
return (unsigned long)mrg_ctx >> MRG_CTX_HEADER_SHIFT;
return (unsigned long)mrg_ctx & ((1 << MRG_CTX_HEADER_SHIFT) - 1);