Messages in this thread | | | From | Ingo Molnar <> | Subject | [PATCH 00/11] x86/mm: Implement lockless pgd_alloc()/pgd_free() | Date | Tue, 22 Sep 2015 08:23:30 +0200 |
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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(-)
-- 2.1.4
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