> On Mar 25, 2022, at 12:40 AM, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > I will continue to look at this. A quick check of the fork code shows the > semaphore held in read mode for the duration of the page table copy. Thank you for looking into it. As a side note about fork() for context, and not to distract from the regression at hand... There's some history here where we ran into problems circa 2005 where fork time went linear with the size of shared memory, and that was resolved by letting the pages fault in the child. This was when hugetlb was pretty new (and not used by us) and I see now that the fix explicitly excluded hugetlb. Anyway, we now mostly use vfork(), only fork() in some special cases, and improving just fork wouldn't fix the scalability regression for us. But, it does sound like fork() time might be getting large again now that everyone is using very large shared segments with hugetlb, but generally haven't switched to 1GB pages. That old thread is: https://lkml.org/lkml/2005/8/24/190
