On Tue, Oct 5, 2021 at 11:42 AM Pavel Machek <pavel@xxxxxx> wrote: > > On Fri 2021-10-01 13:56:57, Suren Baghdasaryan wrote: > > While forking a process with high number (64K) of named anonymous vmas the > > overhead caused by strdup() is noticeable. Experiments with ARM64 > Android > > I still believe you should simply use numbers and do the > numbers->strings mapping in userspace. We should not need to optimize > strdups in kernel... Here are complications with mapping numbers to strings in the userspace: Approach 1: hardcode number->string in some header file and let all tools use that mapping. The issue is that whenever that mapping changes all the tools that are using it (including 3rd party ones) have to be rebuilt. This is not really maintainable since we don't control 3rd party tools and even for the ones we control, it will be a maintenance issue figuring out which version of the tool used which header file. Approach 2: have a centralized facility (a process or a DB) maintaining number->string mapping. This would require an additional request to this facility whenever we want to make a number->string conversion. Moreover, when we want to name a VMA, we would have to register a new VMA name in that facility or check that one already exists and get its ID. So each prctl() call to name a VMA will be preceded by such a request (IPC call), maybe with some optimizations to cache already known number->string pairs. This would be quite expensive performance-wise. Additional issue with this approach is that this mapping will have to be persistent to handle a case when the facility crashes and has to be restored. As I said before, it complicates userspace quite a bit. Is that a good enough reason to store the names in the kernel and pay a little more memory for that? IMHO yes, but I might be wrong. Thanks, Suren. > > Best regards, > Pavel > -- > http://www.livejournal.com/~pavelmachek > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx.
