On Thu, May 17, 2018 at 12:56 PM, Matthew Wilcox <[email protected]> wrote: > On Thu, May 17, 2018 at 12:32:07PM -0700, Dan Williams wrote: >> On Thu, May 17, 2018 at 11:37 AM, Matthew Wilcox <[email protected]> wrote: >> > >> > I plucked this patch from my XArray work. It seems self-contained enough >> > that it could go into the DAX tree for merging this cycle. >> > >> > From 8cb56f4ba36af38814ca7b8ba030a66384e59a21 Mon Sep 17 00:00:00 2001 >> > From: Matthew Wilcox <[email protected]> >> > Date: Thu, 29 Mar 2018 22:41:18 -0400 >> > Subject: [PATCH] dax: Fix use of zero page >> > >> > Use my_zero_pfn instead of ZERO_PAGE, and pass the vaddr to it so it >> > works on MIPS and s390. >> > >> > Signed-off-by: Matthew Wilcox <[email protected]> >> >> I'm being thick and / or lazy, what's the user visible effect of this fix? > > For s390 it appears to be a performance issue: > > Author: Martin Schwidefsky <[email protected]> > Date: Mon Oct 25 16:10:07 2010 +0200 > > [S390] zero page cache synonyms > > If the zero page is mapped to virtual user space addresses that differ > only in bit 2^12 or 2^13 we get L1 cache synonyms which can affect > performance. Follow the mips model and use multiple zero pages to avoid > the synonyms. > > MIPS' use of multiple ZERO_PAGEs predates git history. Given the > history of MIPS' caches behaving in incredibly weird ways, I'd assume > that getting this wrong results in miniature black holes forming and/or > the CPU calculating the largest prime number.
Unless I am missing something I think this sounds like 4.18-rc1 material with a cc: stable. Last I heard no one is really using dccssblk + dax, and MIPS has no way to describe pmem outside of memmap= which is only a development tool. _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
