From: monnier@iro.umontreal.ca   
      
   Kent Dickey [2025-10-03 16:18:47] wrote:   
   > Fork is not a problem with virtual tagged caches or SAS.  Normal fork   
   > starts the child with a copy of the parent's address mapping, and uses   
   > "Copy on Write" (COW) to create unique pages as soon as either process   
   > does a write.   
      
   The problem is not how/when you do the "copy", but the fact that once   
   the data at address A has been changed, address A in the child process   
   and address A in the parent don't contain the same value.  This is   
   fundamentally at odds with SASOS and with virtually-indexed&tagged   
   caches.  The usual workaround is to augment the virtual addresses with   
   some kind of "address-space ID" (ASID).   
      
   That in turn makes it harder to share read-write memory between   
   processes (Mill's approach tried to accommodate that by augmenting only   
   *some* addresses with an ASID, but not all), and requires flushing the   
   cache when an ASID is re-used for another process (which can happen   
   rather often because the size of the ASID is usually limited to a small   
   number of bits).   
      
      
           Stefan   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)