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I wanted to give >>>>> some quick feedback: >>>>> >>>> >>>> Are you seeing improvements with the patchset? >>>> >>> >>> We're nowhere near stable yet, but basic testing shows that CPU time >>> from the start of migrate_vma_* to the end drops from ~300µs to ~6µs on >>> a 2MB GPU fault. A lot of this improvement is dma-mapping at 2M >>> grainularity for the CPU<->GPU copy rather than mapping 512 4k pages >>> too. >>> >>>>> - You appear to have missed updating hmm_range_fault, specifically >>>>> hmm_vma_handle_pmd, to check for device-private entries and populate the >>>>> HMM PFNs accordingly. My colleague François has a fix for this if you're >>>>> interested. >>>>> >>>> >>>> Sure, please feel free to post them. >>>> >>>>> - I believe copy_huge_pmd also needs to be updated to avoid installing a >>>>> migration entry if the swap entry is device-private. I don't have an >>>>> exact fix yet due to my limited experience with core MM. The test case >>>>> that triggers this is fairly simple: fault in a 2MB device page on the >>>>> GPU, then fork a process that reads the page — the kernel crashes in >>>>> this scenario. >>>>> >>>> >>>> I'd be happy to look at any traces you have or post any fixes you have >>>> >>> >>> I've got it so the kernel doesn't explode but still get warnings like: >>> >>> [ 3564.850036] mm/pgtable-generic.c:54: bad pmd ffff8881290408e0(efffff80042bfe00) >>> [ 3565.298186] BUG: Bad rss-counter state mm:ffff88810a100c40 type:MM_ANONPAGES val:114688 >>> [ 3565.306108] BUG: non-zero pgtables_bytes on freeing mm: 917504 >>> >>> I'm basically just skip is_swap_pmd clause if the entry is device >>> private, and let the rest of the function execute. This avoids >>> installing a migration entry—which isn't required and cause the >>> crash—and allows the rmap code to run, which flips the pages to not >>> anonymous exclusive (effectively making them copy-on-write (?), though >>> that doesn't fully apply to device pages). It's not 100% correct yet, >>> but it's a step in the right direction. >>> >> >> >> Thanks, could you post the stack trace as well. This is usually a symptom of >> not freeing up the page table cleanly. >> > > Did you see my reply here [1]? I've got this working cleanly. > > I actually have all my tests passing with a few additional core MM > changes. I'll reply shortly to a few other patches with those details > and will also send over a complete set of the core MM changes we've made > to get things stable. > > Matt > > [1] https://lore.kernel.org/linux-mm/aHrsdvjjliBBdVQm@lstrano-desk.jf.intel.com/ Sorry I missed it. Checking now! I'd be happy to hear any numbers you have. In my throughput tests that rely on page copying (lib/test_hmm.c), I am seeing a 500% improvement in performance and a 80% improvement in latency Thanks, Balbir