Fixes phpGH-8646 See php#8646 for thorough discussion. Interned strings that hold class entries can get a corresponding slot in map_ptr for the CE cache. map_ptr works like a bump allocator: there is a counter which increases to allocate the next slot in the map. For class name strings in non-opcache we have: - on startup: permanent + interned - on request: interned For class name strings in opcache we have: - on startup: permanent + interned - on request: either not interned at all, which we can ignore because they won't get a CE cache entry or they were already permanent + interned or we get a new permanent + interned string in the opcache persistence code Notice that the map_ptr layout always has the permanent strings first, and the request strings after. In non-opcache, a request string may get a slot in map_ptr, and that interned request string gets destroyed at the end of the request. The corresponding map_ptr slot can thereafter never be used again. This causes map_ptr to keep reallocating to larger and larger sizes. We solve it as follows: We can check whether we had any interned request strings, which only happens in non-opcache. If we have any, we reset map_ptr to the last permanent string. We can't lose any permanent strings because of map_ptr's layout.

Commits

Commits on Mar 6, 2023

Fix GH-8646: Memory leak PHP FPM 8.1