On 03/01/2016 01:44 PM, Matthew Wilcox wrote: > On Tue, Mar 01, 2016 at 11:25:41AM +0100, Jan Kara wrote: >> On Tue 01-03-16 02:09:11, Matthew Wilcox wrote: >>> There are a few issues around 1GB THP support that I've come up against >>> while working on DAX support that I think may be interesting to discuss >>> in person. >>> >>> - Do we want to add support for 1GB THP for anonymous pages? DAX support >>> is driving the initial 1GB THP support, but would anonymous VMAs also >>> benefit from 1GB support? I'm not volunteering to do this work, but >>> it might make an interesting conversation if we can identify some users >>> who think performance would be better if they had 1GB THP support. >> >> Some time ago I was thinking about 1GB THP and I was wondering: What is the >> motivation for 1GB pages for persistent memory? Is it the savings in memory >> used for page tables? Or is it about the cost of fault? > > I think it's both. I heard from one customer who calculated that with > a 6TB server, mapping every page into a process would take ~24MB of > page tables. Multiply that by the 50,000 processes they expect to run > on a server of that size consumes 1.2TB of DRAM. Using 1GB pages reduces > that by a factor of 512, down to 2GB. > > Another topic to consider then would be generalising the page table > sharing code that is currently specific to hugetlbfs. I didn't bring > it up as I haven't researched it in any detail, and don't know how hard > it would be. Well, I have started down that path and have it working for some very simple cases with some very hacked up code. Too early/ugly to share. I'm struggling a bit with fact that you can have both regular and huge page mappings of the same regions. The hugetlb code only has to deal with huge pages. -- Mike Kravetz -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>