Re: [PATCH v5] mm: support madvise(MADV_FREE)
From: Rik van Riel
Date: Fri May 09 2014 - 11:15:18 EST
On 05/09/2014 02:28 AM, Minchan Kim wrote:
On Fri, May 09, 2014 at 03:17:14PM +0900, Minchan Kim wrote:
Hello Rik,
On Thu, May 08, 2014 at 04:04:33PM -0400, Rik van Riel wrote:
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.
Thanks!
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.
Hmm, I didn't notice that. Thanks Rik.
Maybe I need this in asm-generic.
static inline void ptep_set_lazyfree(struct mm_struct *mm, unsigned addr, pte_t *ptep)
{
pte_t ptent = *ptep;
ptent = pte_mkold(ptent);
ptent = pte_mkclean(ptent);
set_pte_at(mm, addr, ptep, ptent);
}
For arch/powerpc/include/asm/pgtable.h
static inline void ptep_set_lazyfree(struct mm_struct *mm, unsigned long addr,
pte_t *ptep)
{
pte_update(mm, addr, ptep, _PAGE_DIRTY|_PAGE_ACCESSED, 0, 0);
}
@@ -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.
Oops, the check should have been lazyfree_range.
Will fix.
Now that I see the code, madvise_vma always pass *a* vma so madvise_lazyfree
doesn't cover multiple vma all at once so the current sematic is same with
dontneed. So, I don't see any problem. If I miss something, let me know it.
Does that mean lazyfree_range is unnecessary, and everything
can be done inside lazyfree_single_vma ?
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