Re: [PATCH v10 7/7] mm: Don't split THP page when syscall is called
From: Minchan Kim
Date: Tue Jul 08 2014 - 02:10:32 EST
On Tue, Jul 08, 2014 at 10:30:38AM +0900, Minchan Kim wrote:
> On Mon, Jul 07, 2014 at 02:13:03PM +0300, Kirill A. Shutemov wrote:
> > On Mon, Jul 07, 2014 at 09:53:58AM +0900, Minchan Kim wrote:
> > > We don't need to split THP page when MADV_FREE syscall is
> > > called. It could be done when VM decide really frees it so
> > > we could reduce the number of THP split.
> > >
> > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> > > ---
> > > include/linux/huge_mm.h | 3 +++
> > > mm/huge_memory.c | 25 +++++++++++++++++++++++++
> > > mm/madvise.c | 19 +++++++++++++++++--
> > > mm/rmap.c | 4 ++++
> > > mm/vmscan.c | 24 ++++++++++++++++--------
> > > 5 files changed, 65 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > > index 63579cb8d3dc..f0d37238cf8f 100644
> > > --- a/include/linux/huge_mm.h
> > > +++ b/include/linux/huge_mm.h
> > > @@ -19,6 +19,9 @@ extern struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
> > > unsigned long addr,
> > > pmd_t *pmd,
> > > unsigned int flags);
> > > +extern int madvise_free_pmd(struct mmu_gather *tlb,
> > > + struct vm_area_struct *vma,
> > > + pmd_t *pmd, unsigned long addr);
> > > extern int zap_huge_pmd(struct mmu_gather *tlb,
> > > struct vm_area_struct *vma,
> > > pmd_t *pmd, unsigned long addr);
> > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > > index 5d562a9fe931..2a70069dcfc0 100644
> > > --- a/mm/huge_memory.c
> > > +++ b/mm/huge_memory.c
> > > @@ -1384,6 +1384,31 @@ out:
> > > return 0;
> > > }
> > >
> > > +int madvise_free_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> > > + pmd_t *pmd, unsigned long addr)
> > > +{
> > > + spinlock_t *ptl;
> > > + int ret = 0;
> > > +
> > > + if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> > > + pmd_t orig_pmd;
> > > + struct mm_struct *mm = vma->vm_mm;
> > > +
> > > + /* No hugepage in swapcache */
> > > + VM_BUG_ON(PageSwapCache(pmd_page(orig_pmd)));
> >
> > VM_BUG_ON_PAGE() ?
>
> NP.
>
> >
> > > +
> > > + orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
> > > + orig_pmd = pmd_mkold(orig_pmd);
> > > + orig_pmd = pmd_mkclean(orig_pmd);
> > > +
> > > + set_pmd_at(mm, addr, pmd, orig_pmd);
> > > + tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
> > > + spin_unlock(ptl);
> > > + ret = 1;
> > > + }
> > > + return ret;
> > > +}
> > > +
> > > int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> > > pmd_t *pmd, unsigned long addr)
> > > {
> > > diff --git a/mm/madvise.c b/mm/madvise.c
> > > index 372a25a8ea82..3c99919ee094 100644
> > > --- a/mm/madvise.c
> > > +++ b/mm/madvise.c
> > > @@ -320,8 +320,23 @@ static inline unsigned long madvise_free_pmd_range(struct mmu_gather *tlb,
> > > * if the range covers.
> > > */
> > > next = pmd_addr_end(addr, end);
> > > - if (pmd_trans_huge(*pmd))
> > > - split_huge_page_pmd(vma, addr, pmd);
> > > + if (pmd_trans_huge(*pmd)) {
> > > + if (next - addr != HPAGE_PMD_SIZE) {
> > > +#ifdef CONFIG_DEBUG_VM
> > > + if (!rwsem_is_locked(&tlb->mm->mmap_sem)) {
> > > + pr_err("%s: mmap_sem is unlocked! addr=0x%lx end=0x%lx vma->vm_start=0x%lx vma->vm_end=0x%lx\n",
> > > + __func__, addr, end,
> > > + vma->vm_start,
> > > + vma->vm_end);
> > > + BUG();
> > > + }
> > > +#endif
> > > + split_huge_page_pmd(vma, addr, pmd);
> > > + } else if (madvise_free_pmd(tlb, vma, pmd, addr))
> > > + goto next;
> > > + /* fall through */
> > > + }
> > > +
> > > /*
> > > * Here there can be other concurrent MADV_DONTNEED or
> > > * trans huge page faults running, and if the pmd is
> > > diff --git a/mm/rmap.c b/mm/rmap.c
> > > index ee495d84c8b3..3c415eb8b6f0 100644
> > > --- a/mm/rmap.c
> > > +++ b/mm/rmap.c
> > > @@ -702,6 +702,10 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
> > > /* go ahead even if the pmd is pmd_trans_splitting() */
> > > if (pmdp_clear_flush_young_notify(vma, address, pmd))
> > > referenced++;
> > > +
> > > + if (pmd_dirty(*pmd))
> > > + dirty++;
> > > +
> > > spin_unlock(ptl);
> > > } else {
> > > pte_t *pte;
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index f7a45600846f..4e15babf4414 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -971,15 +971,23 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> > > * Anonymous process memory has backing store?
> > > * Try to allocate it some swap space here.
> > > */
> > > - if (PageAnon(page) && !PageSwapCache(page) && !freeable) {
> > > - if (!(sc->gfp_mask & __GFP_IO))
> > > - goto keep_locked;
> > > - if (!add_to_swap(page, page_list))
> > > - goto activate_locked;
> > > - may_enter_fs = 1;
> > > + if (PageAnon(page) && !PageSwapCache(page)) {
> > > + if (!freeable) {
> > > + if (!(sc->gfp_mask & __GFP_IO))
> > > + goto keep_locked;
> > > + if (!add_to_swap(page, page_list))
> > > + goto activate_locked;
> > > + may_enter_fs = 1;
> > >
> > > - /* Adding to swap updated mapping */
> > > - mapping = page_mapping(page);
> > > + /* Adding to swap updated mapping */
> > > + mapping = page_mapping(page);
> > > + } else {
> > > + if (unlikely(PageTransHuge(page))) {
> > > + if (unlikely(split_huge_page_to_list(
> > > + page, page_list)))
> > > + goto keep_locked;
> >
> > Hm. It would be better to free the huge page without splitting.
> > It shouldn't be a big deal: walk over rmap and zap all pmds.
> > Or I miss something?
>
> Actually, I did but found no problem except CONFIG_DEBUG_VM but rollback
> after peeking [1].
> When I read the description in detail by your review, I think we can remove
> BUG_ON(PageTransHuge(page)) in try_to_unmap and go with no split for lazyfree
> page because they are not in swapcache any more so the assumption of [1] is
> not valid. Will do it in next revision.
>
> Thanks for the review, Kirill!
>
> [1] thp: split_huge_page paging, 3f04f62f9
I just respin without this part because it needs more review but
no enough time to me at the moment.
Nontheless, I want to get review other parts from community.
It's like one of optimization so I think it shouldn't a party pooper.
But finally I will have a time to see that.(ie, I just added some
comment to make try_to_unmap be aware of THP freeing)
Thanks for the review!
--
Kind regards,
Minchan Kim
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