The problem is some of the alternatives seem to be suggested by way of "if we had any support for this it would be better than O_DIRECT". So don't use O_DIRECT,

The problem is some of the alternatives seem to be suggested by way of "if we had any support for this it would be better than O_DIRECT". So don't use O_DIRECT, use the alternative which doesn't exist, is still too slow, only covers parts of what you need, etc. .