diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/mm.h | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index d78e294698b0..ab2e7e30aef9 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -4208,6 +4208,15 @@ static inline void clear_page_guard(struct zone *zone, struct page *page, * mapped to user space. * * Does absolutely no exception handling. + * + * Note that even though the clearing operation is preemptible, clear_pages() + * does not (and on architectures where it reduces to a few long-running + * instructions, might not be able to) call cond_resched() to check if + * rescheduling is required. + * + * When running under preemptible models this is not a problem. Under + * cooperatively scheduled models, however, the caller is expected to + * limit @npages to no more than PROCESS_PAGES_NON_PREEMPT_BATCH. */ static inline void clear_pages(void *addr, unsigned int npages) { @@ -4218,6 +4227,32 @@ static inline void clear_pages(void *addr, unsigned int npages) } #endif +#ifndef PROCESS_PAGES_NON_PREEMPT_BATCH +#ifdef clear_pages +/* + * The architecture defines clear_pages(), and we assume that it is + * generally "fast". So choose a batch size large enough to allow the processor + * headroom for optimizing the operation and yet small enough that we see + * reasonable preemption latency for when this optimization is not possible + * (ex. slow microarchitectures, memory bandwidth saturation.) + * + * With a value of 32MB and assuming a memory bandwidth of ~10GBps, this should + * result in worst case preemption latency of around 3ms when clearing pages. + * + * (See comment above clear_pages() for why preemption latency is a concern + * here.) + */ +#define PROCESS_PAGES_NON_PREEMPT_BATCH (SZ_32M >> PAGE_SHIFT) +#else /* !clear_pages */ +/* + * The architecture does not provide a clear_pages() implementation. Assume + * that clear_page() -- which clear_pages() will fallback to -- is relatively + * slow and choose a small value for PROCESS_PAGES_NON_PREEMPT_BATCH. + */ +#define PROCESS_PAGES_NON_PREEMPT_BATCH 1 +#endif +#endif + #ifdef __HAVE_ARCH_GATE_AREA extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm); extern int in_gate_area_no_mm(unsigned long addr); |