On Fri 28 Jun 2019 05:09:11 PM CEST, Kevin Wolf wrote: > Am 28.06.2019 um 17:02 hat Alberto Garcia geschrieben: >> On Fri 28 Jun 2019 04:57:08 PM CEST, Kevin Wolf wrote: >> > Am 28.06.2019 um 16:43 hat Alberto Garcia geschrieben: >> >> On Thu 27 Jun 2019 06:05:55 PM CEST, Denis Lunev wrote: >> >> > Please note, I am not talking now about your case with COW. Here the >> >> > allocation is performed on the sub-cluster basis, i.e. the abscence of >> >> > the sub-cluster in the image means hole on that offset. This is >> >> > important difference. >> >> >> >> I mentioned the possibility that if you have a case like 2MB / 64KB >> >> and you write to an empty cluster then you could allocate the >> >> necessary subclusters, and additionally fallocate() the space of the >> >> whole cluster (2MB) in order to try to keep it contiguous. >> >> >> >> With this we would lose the space saving advantage of having >> >> subclusters. But perhaps that would work for smaller cluster sizes >> >> (it would mitigate the fragmentation problem). >> > >> > There seem to be use cases for both ways. So does this need to be an >> > option? >> >> Probably a runtime option, or a heuristic that decides what to do >> depending on the cluster size. > > How would the heuristic decide whether the user wants to save disk space > or whether they consider avoiding fragmentation (i.e. performance) more > important?
Well I suppose the fragmentation problem is more important when you have small clusters and less so when you have large clusters, so that would be a way to do it. Of course with an option the user would have the final choice. Berto
