<story><title>Remove PG_ZERO and zeroidle (page-zeroing) entirely</title><url>http://lists.dragonflybsd.org/pipermail/commits/2016-August/624202.html</url></story><parent_chain></parent_chain><comment><author>jdub</author><text>When a program needs memory, the operating system maps a physical page of memory (4KB in most cases) into its virtual memory space.&lt;p&gt;That page might have been in use by a different program only moments before, so the new program could go poking around in it to find interesting stuff. Like SSH keys or passwords or whatever. So the operating system has a responsibility to tidy up pre-loved pages before giving them out.&lt;p&gt;Once upon a time, filling 4KB with zeroes was a costly operation. It took a bunch of CPU cycles, and worse, would have trashed memory caches closer to the CPU.&lt;p&gt;So operating systems tend to have queues of discarded pages, background threads to zero them (when nothing more important is happening), and queues of zeroed pages to hand out when a program wants more memory.&lt;p&gt;This change is DragonFly BSD saying, &amp;quot;Fuck it, we&amp;#x27;ll do it live&amp;quot;. It turns out that with the speed of modern CPUs and the way memory caches work today, they reckon it&amp;#x27;s faster to just zero the memory synchronously, when the program requests it. No more queues, no more background work, no more weird cache behaviour.</text></comment>
<story><title>Remove PG_ZERO and zeroidle (page-zeroing) entirely</title><url>http://lists.dragonflybsd.org/pipermail/commits/2016-August/624202.html</url></story><parent_chain></parent_chain><comment><author>blinkingled</author><text>DragonFlyBSD is slowly but steadily becoming more attractive as a Linux&amp;#x2F;FreeBSD alternative. 4.6 has good support for various newer Intel GPUs, hammer is stable and the SMP and Networking performance is stellar.&lt;p&gt;I had a 2.8TB backup archive that I have repeatedly tried to dedup with ZFS and the realtime while-you-are-writing architecture of ZFS dedup just kills the performance so badly that I have never actually succeeded going over the full dataset. Past week I made a 4.6-rc2 based DragonFly VM, attached a 3TB disk with RDM, formatted it with HAMMER, started rsync of the backed up data and ran hammer dedup every 30 min - I am now at 1.9TB used after the whole thing was done and a final dedup ran - no noticeable speed drops and I got around 900GB back!</text></comment>