[PATCH 00/11] x86/mm: Implement lockless pgd_alloc()/pgd_free()

Ingo Molnar
2015-09-22T06:24:25Z

So this is the somewhat belated latest iteration of the series.
I (think I) fixed all correctness bugs in the code pointed out by Oleg.

The task list walk is still 'dumb', using for_each_process(), as none of
the call sites are performance critical.

Oleg, can you see any problems with this code?

Background:

Waiman Long reported 'pgd_lock' contention on high CPU count systems and proposed
moving pgd_lock on a separate cacheline to eliminate false sharing and to reduce
some of the lock bouncing overhead.

I think we can do much better: this series eliminates the pgd_list and makes
pgd_alloc()/pgd_free() lockless.

Now the lockless initialization of the PGD has a few preconditions, which the
initial part of the series implements:

- no PGD clearing is allowed, only additions. This makes sense as a single PGD
entry covers 512 GB of RAM so the 4K overhead per 0.5TB of RAM mapped is
miniscule.

The patches after that convert existing pgd_list users to walk the task list.

PGD locking is kept intact: coherency guarantees between the CPA, vmalloc,
hotplug, etc. code are unchanged.

The final patches eliminate the pgd_list and thus make pgd_alloc()/pgd_free()
lockless.

The patches have been boot tested on 64-bit and 32-bit x86 systems.

Architectures not making use of the new facility are unaffected.

Thanks,

Ingo

===
Ingo Molnar (11):
x86/mm/pat: Don't free PGD entries on memory unmap
x86/mm/hotplug: Remove pgd_list use from the memory hotplug code
x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()
x86/mm/hotplug: Simplify sync_global_pgds()
mm: Introduce arch_pgd_init_late()
x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code
x86/mm: Remove pgd_list use from vmalloc_sync_all()
x86/mm/pat/32: Remove pgd_list use from the PAT code
x86/mm: Make pgd_alloc()/pgd_free() lockless
x86/mm: Remove pgd_list leftovers
x86/mm: Simplify pgd_alloc()

arch/Kconfig | 9 +++
arch/x86/Kconfig | 1 +
arch/x86/include/asm/pgtable.h | 3 -
arch/x86/include/asm/pgtable_64.h | 3 +-
arch/x86/mm/fault.c | 32 +++++++---
arch/x86/mm/init_64.c | 92 ++++++++++++--------------
arch/x86/mm/pageattr.c | 40 ++++++------
arch/x86/mm/pgtable.c | 131 +++++++++++++++++++-------------------
arch/x86/xen/mmu.c | 45 +++++++++++--
fs/exec.c | 3 +
include/linux/mm.h | 6 ++
kernel/fork.c | 16 +++++
12 files changed, 227 insertions(+), 154 deletions(-)

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2.1.4