On Fri, Nov 20, 2020 at 12:18:22PM +0100, Christophe Leroy wrote: > Hi Peter, > > Le 13/11/2020 à 14:44, Christophe Leroy a écrit : > > Hi > > > > Le 13/11/2020 à 12:19, Peter Zijlstra a écrit : > > > Hi, > > > > > > These patches provide generic infrastructure to determine TLB page size from > > > page table entries alone. Perf will use this (for either data or code address) > > > to aid in profiling TLB issues. > > > > > > While most architectures only have page table aligned large pages, some > > > (notably ARM64, Sparc64 and Power) provide non page table aligned large pages > > > and need to provide their own implementation of these functions. > > > > > > I've provided (completely untested) implementations for ARM64 and Sparc64, but > > > failed to penetrate the _many_ Power MMUs. I'm hoping Nick or Aneesh can help > > > me out there. > > > > > > > I can help with powerpc 8xx. It is a 32 bits powerpc. The PGD has 1024 > > entries, that means each entry maps 4M. > > > > Page sizes are 4k, 16k, 512k and 8M. > > > > For the 8M pages we use hugepd with a single entry. The two related PGD > > entries point to the same hugepd. > > > > For the other sizes, they are in standard page tables. 16k pages appear > > 4 times in the page table. 512k entries appear 128 times in the page > > table. > > > > When the PGD entry has _PMD_PAGE_8M bits, the PMD entry points to a > > hugepd with holds the single 8M entry. > > > > In the PTE, we have two bits: _PAGE_SPS and _PAGE_HUGE > > > > _PAGE_HUGE means it is a 512k page > > _PAGE_SPS means it is not a 4k page > > > > The kernel can by build either with 4k pages as standard page size, or > > 16k pages. It doesn't change the page table layout though. > > > > Hope this is clear. Now I don't really know to wire that up to your series. > > Does my description make sense ? Is there anything I can help with ? It did, and I had vague memories from when we fixed that pgd_t issue. I've just not had time to dig through the powerpc code yet to find the right mmu header to stick it in. I was meaning to get another version of these patches posted this week, but time keeps slipping away, I'll try.
