Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Uros Bizjak <> | Subject | [PATCH 3/3] iommufd: Use atomic_long_try_cmpxchg() in incr_user_locked_vm() | Date | Wed, 22 May 2024 10:26:49 +0200 |
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Use atomic_long_try_cmpxchg() instead of atomic_long_cmpxchg (*ptr, old, new) != old in incr_user_locked_vm(). cmpxchg returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg).
Also, atomic_long_try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kevin Tian <kevin.tian@intel.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Will Deacon <will@kernel.org> Cc: Robin Murphy <robin.murphy@arm.com> --- drivers/iommu/iommufd/pages.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/iommu/iommufd/pages.c b/drivers/iommu/iommufd/pages.c index 528f356238b3..117f644a0c5b 100644 --- a/drivers/iommu/iommufd/pages.c +++ b/drivers/iommu/iommufd/pages.c @@ -809,13 +809,14 @@ static int incr_user_locked_vm(struct iopt_pages *pages, unsigned long npages) lock_limit = task_rlimit(pages->source_task, RLIMIT_MEMLOCK) >> PAGE_SHIFT; + + cur_pages = atomic_long_read(&pages->source_user->locked_vm); do { - cur_pages = atomic_long_read(&pages->source_user->locked_vm); new_pages = cur_pages + npages; if (new_pages > lock_limit) return -ENOMEM; - } while (atomic_long_cmpxchg(&pages->source_user->locked_vm, cur_pages, - new_pages) != cur_pages); + } while (!atomic_long_try_cmpxchg(&pages->source_user->locked_vm, + &cur_pages, new_pages)); return 0; } -- 2.45.1
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