On 04/20/2014 09:56 PM, Minchan Kim wrote:
In summary, MADV_FREE is about 2 time faster than MADV_DONTNEED.
This is awesome.
I have a few nitpicks with the patch, though :)
+static long madvise_lazyfree(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ *prev = vma;
+ if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
+ return -EINVAL;
+
+ /* MADV_FREE works for only anon vma at the moment */
+ if (vma->vm_file)
+ return -EINVAL;
+
+ lazyfree_range(vma, start, end - start);
+ return 0;
+}
This code checks whether lazyfree_range would work on
the VMA...
diff --git a/mm/memory.c b/mm/memory.c
index c4b5bc250820..ca427f258204 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1270,6 +1270,104 @@ static inline unsigned long zap_pud_range(struct
mmu_gather *tlb,
return addr;
}
+static unsigned long lazyfree_pte_range(struct mmu_gather *tlb,
+ struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long addr, unsigned long end)
+{
+ struct mm_struct *mm = tlb->mm;
+ spinlock_t *ptl;
+ pte_t *start_pte;
+ pte_t *pte;
+
+ start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ pte = start_pte;
+ arch_enter_lazy_mmu_mode();
+ do {
+ pte_t ptent = *pte;
+
+ if (pte_none(ptent))
+ continue;
+
+ if (!pte_present(ptent))
+ continue;
+
+ ptent = pte_mkold(ptent);
+ ptent = pte_mkclean(ptent);
+ set_pte_at(mm, addr, pte, ptent);
+ tlb_remove_tlb_entry(tlb, pte, addr);
This may not work on PPC, which has a weird hash table for
its TLB. You will find that tlb_remove_tlb_entry does
nothing for PPC64, and set_pte_at does not remove the hash
table entry either.
@@ -1370,6 +1485,31 @@ void unmap_vmas(struct mmu_gather *tlb,
}
/**
+ * lazyfree_range - clear dirty bit of pte in a given range
+ * @vma: vm_area_struct holding the applicable pages
+ * @start: starting address of pages
+ * @size: number of bytes to do lazyfree
+ *
+ * Caller must protect the VMA list
+ */
+void lazyfree_range(struct vm_area_struct *vma, unsigned long start,
+ unsigned long size)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ struct mmu_gather tlb;
+ unsigned long end = start + size;
+
+ lru_add_drain();
+ tlb_gather_mmu(&tlb, mm, start, end);
+ update_hiwater_rss(mm);
+ mmu_notifier_invalidate_range_start(mm, start, end);
+ for ( ; vma && vma->vm_start < end; vma = vma->vm_next)
+ lazyfree_single_vma(&tlb, vma, start, end);
+ mmu_notifier_invalidate_range_end(mm, start, end);
+ tlb_finish_mmu(&tlb, start, end);
+}
This function, called by madvise_lazyfree, can iterate
over multiple VMAs.
However, madvise_lazyfree only checked one of them.
What should happen when the code encounters a VMA where
MADV_FREE does not work? Should it return an error?
Should it skip over it?
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