TYPO3 Core

Currently the activation of the APC-Preset in the Install Tool is only available under the following conditions:

1. The APC extensions is loaded
2. The configured cache size is configured to have at least 100 MB of shared memory
3. The cache has at least 5 MB free memory

The memory required by the Extbase object cache is actually very small (at 6.2: ~250 KB, at 7.6: ~2,5 MB, with no extra extensions installed).

I would propose, dropping the 2. condition, because a large portion of the reserved memory will never be used. After all on shared hosting environments the configured memory size is usually limited, and enabling the APCu backend is not possible in this cases. Anyway it is slightly nonsense to check the configured total size, whereas the available free memory is relevant – what indeed will be ensured by the 3. condition.

Maybe it would also be reasonable to raise the required free memory up to 10 MB (3. condition), to have some space in reserve for potentially installed extensions.