[HN Gopher] The trouble with 64-bit DMA in Linux
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       The trouble with 64-bit DMA in Linux
        
       Author : chmaynard
       Score  : 10 points
       Date   : 2022-08-11 15:45 UTC (1 days ago)
        
 (HTM) web link (lwn.net)
 (TXT) w3m dump (lwn.net)
        
       | jasoneckert wrote:
       | "One of the core rules of kernel development is that good things
       | rarely result from breaking Linus Torvalds's machine..." sums up
       | this post beautifully.
        
       | wrs wrote:
       | This is a tangent, but I was reminded of early Macintosh days,
       | where the 68000 processor in the original Mac hardware only paid
       | attention to the lower 24 bits of addresses, and only the lower
       | 22 were actually connected to memory. The heap manager used the
       | upper bits of pointers as a convenient place to store flags, and
       | didn't bother zeroing them on dereference because they were
       | ignored anyway.
       | 
       | The release of the 68020 and Macs with more RAM resulted in the
       | need for a whole transition to "32-bit clean" system and apps
       | that took a while. I also seem to recall something about early
       | versions of Microsoft Mac apps being limited to the lower
       | megabyte of RAM for a similar reason.
        
       | chmaynard wrote:
       | See https://lwn.net/SubscriberLink/904210/46bbced99963b245/
        
         | sophacles wrote:
         | @dang - Can you edit the top link to this subscriber link so
         | folks with out an account at lwn don't have to search the
         | comments please?
         | 
         | Also for everyone else - just a reminder, LWN is a great
         | resource and is funded through subscriptions. Personally, I've
         | found the information on this site to be extremely helpful to
         | understanding how the kernel works - to the point that multiple
         | products I've built were only really doable because of LWN
         | articles explaining the subsystem I'm working with (namespaces,
         | io_uring, etc are all are the topic of fantastic articles
         | there). A personal subscription is extremely affordable and
         | very much worth it. They have corporate site license
         | subscriptions too.
        
         | tuckerpo wrote:
         | Thanks.
        
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       (page generated 2022-08-12 23:00 UTC)