Hi Scott, On 19 December 2017 at 02:16, Scott Bennett via ccache < ccache@lists.samba.org> wrote:
> I set "limit_multiple = 0.95" in ccache.conf and "max_size = 30.0G" > in ccache.conf, but cleanups are triggered when space usage reaches 24 GB, > which is the default of 0.8. Why is this happening with ccache 3.3.4? > The ccache manual is not very good at describing what actually happens at cleanup. I'll try to improve it. Here's how cleanup works: After a cache miss, ccache stores the object file in (a subdirectory of) one of the 16 top level directories in the cache (0-9, a-f). It then checks if that top level directory holds more than max_cache_size/16 bytes (and similar for max_files). If yes, ccache removes files from that top level directory until it contains at most limit_multiple*max_cache_size/16 bytes. This means that if limit_multiple is 0.8, the total cache size is expected to hover around 0.9*max_cache_size when it has filled up. But due to the pseudo-randomness of the hash algorithm, the cache size can be closer to 0.8*max_cache_size or 1.0*max_cache_size. The above should be true for any serial usage of ccache. However, ccache is of course very often called in parallel, and then there is a race condition since several ccache processes that have stored an object to the same top level directory may start the cleanup process simultaneously. Since performing cleanup in a large cache with a low limit_multiple can take a lot of time, more ccache processes may start to perform cleanup of the same directory. The race can lead to the final cache size being below limit_multiple*max_cache_size, perhaps very much so. This is a known problem. We have had some ideas to improve the admittedly naive cleanup logic, but nothing has been done yet. Maybe the above described problem is why you get a 24 GB cache size? Or maybe you ran "ccache -c"? Unlike what the manual indicates, "ccache -c" will delete files until each top level directory holds at most limit_multiple*max_size/16... why is limit_multiple ignored? It isn't. Or don't you see a difference if you e.g. set it to 0.5? -- Joel _______________________________________________ ccache mailing list ccache@lists.samba.org https://lists.samba.org/mailman/listinfo/ccache
