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Subject[patch] sched, mm: fix scheduling latencies in unmap_vmas()

The attached patch fixes long latencies in unmap_vmas(). We had
lockbreak code in that function already but it did not take delayed
effects of TLB-gather into account.

has been tested as part of the -VP patchset.

Ingo

The attached patch fixes long latencies in unmap_vmas(). We had
lockbreak code in that function already but it did not take delayed
effects of TLB-gather into account.

has been tested as part of the -VP patchset.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

--- linux/mm/memory.c.orig
+++ linux/mm/memory.c
@@ -497,19 +497,15 @@ static void unmap_page_range(struct mmu_
tlb_end_vma(tlb, vma);
}

-/* Dispose of an entire struct mmu_gather per rescheduling point */
-#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
-#define ZAP_BLOCK_SIZE (FREE_PTE_NR * PAGE_SIZE)
-#endif
-
-/* For UP, 256 pages at a time gives nice low latency */
-#if !defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
-#define ZAP_BLOCK_SIZE (256 * PAGE_SIZE)
-#endif
-
+#ifdef CONFIG_PREEMPT
+/*
+ * It's not an issue to have a small zap block size - TLB flushes
+ * only happen once normally, due to the tlb->need_flush optimization.
+ */
+# define ZAP_BLOCK_SIZE (8 * PAGE_SIZE)
+#else
/* No preempt: go for improved straight-line efficiency */
-#if !defined(CONFIG_PREEMPT)
-#define ZAP_BLOCK_SIZE (1024 * PAGE_SIZE)
+# define ZAP_BLOCK_SIZE (1024 * PAGE_SIZE)
#endif

/**
@@ -584,15 +580,15 @@ int unmap_vmas(struct mmu_gather **tlbp,

start += block;
zap_bytes -= block;
- if ((long)zap_bytes > 0)
- continue;
- if (!atomic && need_resched()) {
+ if (!atomic) {
int fullmm = tlb_is_full_mm(*tlbp);
tlb_finish_mmu(*tlbp, tlb_start, start);
cond_resched_lock(&mm->page_table_lock);
*tlbp = tlb_gather_mmu(mm, fullmm);
tlb_start_valid = 0;
}
+ if ((long)zap_bytes > 0)
+ continue;
zap_bytes = ZAP_BLOCK_SIZE;
}
}
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