[PATCH 0/6] RCU get_user_pages_fast and __get_user_pages_fast
dann.frazier at canonical.com
Wed Aug 20 07:56:09 PDT 2014
On Wed, Jun 25, 2014 at 9:40 AM, Steve Capper <steve.capper at linaro.org> wrote:
> This series implements general forms of get_user_pages_fast and
> __get_user_pages_fast and activates them for arm and arm64.
> These are required for Transparent HugePages to function correctly, as
> a futex on a THP tail will otherwise result in an infinite loop (due to
> the core implementation of __get_user_pages_fast always returning 0).
> This series may also be beneficial for direct-IO heavy workloads and
> certain KVM workloads.
> The main changes since RFC V5 are:
> * Rebased against 3.16-rc1.
> * pmd_present no longer tested for by gup_huge_pmd and gup_huge_pud,
> because the entry must be present for these leaf functions to be
> * Rather than assume puds can be re-cast as pmds, a separate
> function pud_write is instead used by the core gup.
> * ARM activation logic changed, now it will only activate
> RCU_TABLE_FREE and RCU_GUP when running with LPAE.
> The main changes since RFC V4 are:
> * corrected the arm64 logic so it now correctly rcu-frees page
> table backing pages.
> * rcu free logic relaxed for pre-ARMv7 ARM as we need an IPI to
> invalidate TLBs anyway.
> * rebased to 3.15-rc3 (some minor changes were needed to allow it to merge).
> * dropped Catalin's mmu_gather patch as that's been merged already.
> This series has been tested with LTP and some custom futex tests that
> exacerbate the futex on THP tail case. Also debug counters were
> temporarily employed to ensure that the RCU_TABLE_FREE logic was
> behaving as expected.
> I would really appreciate any testers or comments (especially on the
> validity or otherwise of the core fast_gup implementation).
I have a test case that can reliably hit the THP issue on arm64, which
hits it on both 3.16 and 3.17-rc1. I do a "juju bootstrap local" w/
THP disabled at boot. Then I reboot with THP enabled. At this point
you'll see jujud spin at 200% CPU. gccgo binaries seem to have a nack
for hitting it.
I validated that your patches resolve this issue on 3.16, so:
Tested-by: dann frazier <dann.frazier at canonical.com>
I haven't done the same for 3.17-rc1 because they no longer apply
cleanly, but I'm happy to test future submissions w/ hopefully a
shorter feedback loop (please add me to the CC). btw, should we
consider something like this until your patches go in?
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fd4e81a..820e3d9 100644
@@ -306,6 +306,7 @@ config ARCH_WANT_HUGE_PMD_SHARE
+ depends on BROKEN
> Steve Capper (6):
> mm: Introduce a general RCU get_user_pages_fast.
> arm: mm: Introduce special ptes for LPAE
> arm: mm: Enable HAVE_RCU_TABLE_FREE logic
> arm: mm: Enable RCU fast_gup
> arm64: mm: Enable HAVE_RCU_TABLE_FREE logic
> arm64: mm: Enable RCU fast_gup
> arch/arm/Kconfig | 5 +
> arch/arm/include/asm/pgtable-2level.h | 2 +
> arch/arm/include/asm/pgtable-3level.h | 16 ++
> arch/arm/include/asm/pgtable.h | 6 +-
> arch/arm/include/asm/tlb.h | 38 ++++-
> arch/arm/mm/flush.c | 19 +++
> arch/arm64/Kconfig | 4 +
> arch/arm64/include/asm/pgtable.h | 11 +-
> arch/arm64/include/asm/tlb.h | 18 ++-
> arch/arm64/mm/flush.c | 19 +++
> mm/Kconfig | 3 +
> mm/gup.c | 278 ++++++++++++++++++++++++++++++++++
> 12 files changed, 410 insertions(+), 9 deletions(-)
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