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Date: Wed, 10 Jul 2019 19:56:27 +0900
From: Minchan Kim <minchan@...nel.org>
To: Michal Hocko <mhocko@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
Johannes Weiner <hannes@...xchg.org>,
Tim Murray <timmurray@...gle.com>,
Joel Fernandes <joel@...lfernandes.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Daniel Colascione <dancol@...gle.com>,
Shakeel Butt <shakeelb@...gle.com>,
Sonny Rao <sonnyrao@...gle.com>, oleksandr@...hat.com,
hdanton@...a.com, lizeb@...gle.com,
Dave Hansen <dave.hansen@...el.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v3 5/5] mm: factor out pmd young/dirty bit handling and
THP split
On Tue, Jul 09, 2019 at 04:10:19PM +0200, Michal Hocko wrote:
> On Thu 27-06-19 20:54:05, Minchan Kim wrote:
> > Now, there are common part among MADV_COLD|PAGEOUT|FREE to reset
> > access/dirty bit resetting or split the THP page to handle part
> > of subpages in the THP page. This patch factor out the common part.
>
> While this reduces the code duplication to some degree I suspect it only
> goes half way. I haven't tried that myself due to lack of time but I
> believe this has a potential to reduce even more. All those madvise
> calls are doing the same thing essentially. What page tables and apply
> an operation on ptes and/or a page that is mapped. And that suggests
> that the specific operation should be good with defining two - pte and
> page operations on each entry. All the rest should be a common code.
>
> That being said, I do not feel strongly about this patch. The rest of
> the series should be good enough even without it and I wouldn't delay it
> just by discussing a potential of the cleanup.
I totally agree with you. For several cycles, some people asked me to
factor common part out. I understand them why they wanted it. However,
when I tried it, it's not trivial to clean it out due to subtle
difference of them. If I couldn't make it clean at this moment, I want to
keep them without factoing out since it's more readable, at least.
I will drop this patch next submit unless someone pop with better idea.
>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> > ---
> > include/linux/huge_mm.h | 3 -
> > mm/huge_memory.c | 74 -------------
> > mm/madvise.c | 234 +++++++++++++++++++++++-----------------
> > 3 files changed, 135 insertions(+), 176 deletions(-)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 7cd5c150c21d..2667e1aa3ce5 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -29,9 +29,6 @@ extern struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
> > unsigned long addr,
> > pmd_t *pmd,
> > unsigned int flags);
> > -extern bool madvise_free_huge_pmd(struct mmu_gather *tlb,
> > - struct vm_area_struct *vma,
> > - pmd_t *pmd, unsigned long addr, unsigned long next);
> > 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 93f531b63a45..e4b9a06788f3 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1671,80 +1671,6 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
> > return 0;
> > }
> >
> > -/*
> > - * Return true if we do MADV_FREE successfully on entire pmd page.
> > - * Otherwise, return false.
> > - */
> > -bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> > - pmd_t *pmd, unsigned long addr, unsigned long next)
> > -{
> > - spinlock_t *ptl;
> > - pmd_t orig_pmd;
> > - struct page *page;
> > - struct mm_struct *mm = tlb->mm;
> > - bool ret = false;
> > -
> > - tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
> > -
> > - ptl = pmd_trans_huge_lock(pmd, vma);
> > - if (!ptl)
> > - goto out_unlocked;
> > -
> > - orig_pmd = *pmd;
> > - if (is_huge_zero_pmd(orig_pmd))
> > - goto out;
> > -
> > - if (unlikely(!pmd_present(orig_pmd))) {
> > - VM_BUG_ON(thp_migration_supported() &&
> > - !is_pmd_migration_entry(orig_pmd));
> > - goto out;
> > - }
> > -
> > - page = pmd_page(orig_pmd);
> > - /*
> > - * If other processes are mapping this page, we couldn't discard
> > - * the page unless they all do MADV_FREE so let's skip the page.
> > - */
> > - if (page_mapcount(page) != 1)
> > - goto out;
> > -
> > - if (!trylock_page(page))
> > - goto out;
> > -
> > - /*
> > - * If user want to discard part-pages of THP, split it so MADV_FREE
> > - * will deactivate only them.
> > - */
> > - if (next - addr != HPAGE_PMD_SIZE) {
> > - get_page(page);
> > - spin_unlock(ptl);
> > - split_huge_page(page);
> > - unlock_page(page);
> > - put_page(page);
> > - goto out_unlocked;
> > - }
> > -
> > - if (PageDirty(page))
> > - ClearPageDirty(page);
> > - unlock_page(page);
> > -
> > - if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
> > - pmdp_invalidate(vma, 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);
> > - }
> > -
> > - mark_page_lazyfree(page);
> > - ret = true;
> > -out:
> > - spin_unlock(ptl);
> > -out_unlocked:
> > - return ret;
> > -}
> > -
> > static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
> > {
> > pgtable_t pgtable;
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index ee210473f639..13b06dc8d402 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -310,6 +310,91 @@ static long madvise_willneed(struct vm_area_struct *vma,
> > return 0;
> > }
> >
> > +enum madv_pmdp_reset_t {
> > + MADV_PMDP_RESET, /* pmd was reset successfully */
> > + MADV_PMDP_SPLIT, /* pmd was split */
> > + MADV_PMDP_ERROR,
> > +};
> > +
> > +static enum madv_pmdp_reset_t madvise_pmdp_reset_or_split(struct mm_walk *walk,
> > + pmd_t *pmd, spinlock_t *ptl,
> > + unsigned long addr, unsigned long end,
> > + bool young, bool dirty)
> > +{
> > + pmd_t orig_pmd;
> > + unsigned long next;
> > + struct page *page;
> > + struct mmu_gather *tlb = walk->private;
> > + struct mm_struct *mm = walk->mm;
> > + struct vm_area_struct *vma = walk->vma;
> > + bool reset_young = false;
> > + bool reset_dirty = false;
> > + enum madv_pmdp_reset_t ret = MADV_PMDP_ERROR;
> > +
> > + orig_pmd = *pmd;
> > + if (is_huge_zero_pmd(orig_pmd))
> > + return ret;
> > +
> > + if (unlikely(!pmd_present(orig_pmd))) {
> > + VM_BUG_ON(thp_migration_supported() &&
> > + !is_pmd_migration_entry(orig_pmd));
> > + return ret;
> > + }
> > +
> > + next = pmd_addr_end(addr, end);
> > + page = pmd_page(orig_pmd);
> > + if (next - addr != HPAGE_PMD_SIZE) {
> > + /*
> > + * THP collapsing is not cheap so only split the page is
> > + * private to the this process.
> > + */
> > + if (page_mapcount(page) != 1)
> > + return ret;
> > + get_page(page);
> > + spin_unlock(ptl);
> > + lock_page(page);
> > + if (!split_huge_page(page))
> > + ret = MADV_PMDP_SPLIT;
> > + unlock_page(page);
> > + put_page(page);
> > + return ret;
> > + }
> > +
> > + if (young && pmd_young(orig_pmd))
> > + reset_young = true;
> > + if (dirty && pmd_dirty(orig_pmd))
> > + reset_dirty = true;
> > +
> > + /*
> > + * Other process could rely on the PG_dirty for data consistency,
> > + * not pte_dirty so we could reset PG_dirty only when we are owner
> > + * of the page.
> > + */
> > + if (reset_dirty) {
> > + if (page_mapcount(page) != 1)
> > + goto out;
> > + if (!trylock_page(page))
> > + goto out;
> > + if (PageDirty(page))
> > + ClearPageDirty(page);
> > + unlock_page(page);
> > + }
> > +
> > + ret = MADV_PMDP_RESET;
> > + if (reset_young || reset_dirty) {
> > + tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
> > + pmdp_invalidate(vma, addr, pmd);
> > + if (reset_young)
> > + orig_pmd = pmd_mkold(orig_pmd);
> > + if (reset_dirty)
> > + orig_pmd = pmd_mkclean(orig_pmd);
> > + set_pmd_at(mm, addr, pmd, orig_pmd);
> > + tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
> > + }
> > +out:
> > + return ret;
> > +}
> > +
> > static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
> > unsigned long end, struct mm_walk *walk)
> > {
> > @@ -319,64 +404,31 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
> > pte_t *orig_pte, *pte, ptent;
> > spinlock_t *ptl;
> > struct page *page;
> > - unsigned long next;
> >
> > - next = pmd_addr_end(addr, end);
> > if (pmd_trans_huge(*pmd)) {
> > - pmd_t orig_pmd;
> > -
> > - tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
> > ptl = pmd_trans_huge_lock(pmd, vma);
> > if (!ptl)
> > return 0;
> >
> > - orig_pmd = *pmd;
> > - if (is_huge_zero_pmd(orig_pmd))
> > - goto huge_unlock;
> > -
> > - if (unlikely(!pmd_present(orig_pmd))) {
> > - VM_BUG_ON(thp_migration_supported() &&
> > - !is_pmd_migration_entry(orig_pmd));
> > - goto huge_unlock;
> > - }
> > -
> > - page = pmd_page(orig_pmd);
> > - if (next - addr != HPAGE_PMD_SIZE) {
> > - int err;
> > -
> > - if (page_mapcount(page) != 1)
> > - goto huge_unlock;
> > -
> > - get_page(page);
> > + switch (madvise_pmdp_reset_or_split(walk, pmd, ptl, addr, end,
> > + true, false)) {
> > + case MADV_PMDP_RESET:
> > spin_unlock(ptl);
> > - lock_page(page);
> > - err = split_huge_page(page);
> > - unlock_page(page);
> > - put_page(page);
> > - if (!err)
> > - goto regular_page;
> > - return 0;
> > - }
> > -
> > - if (pmd_young(orig_pmd)) {
> > - pmdp_invalidate(vma, addr, pmd);
> > - orig_pmd = pmd_mkold(orig_pmd);
> > -
> > - set_pmd_at(mm, addr, pmd, orig_pmd);
> > - tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
> > + page = pmd_page(*pmd);
> > + test_and_clear_page_young(page);
> > + deactivate_page(page);
> > + goto next;
> > + case MADV_PMDP_ERROR:
> > + spin_unlock(ptl);
> > + goto next;
> > + case MADV_PMDP_SPLIT:
> > + ; /* go through */
> > }
> > -
> > - test_and_clear_page_young(page);
> > - deactivate_page(page);
> > -huge_unlock:
> > - spin_unlock(ptl);
> > - return 0;
> > }
> >
> > if (pmd_trans_unstable(pmd))
> > return 0;
> >
> > -regular_page:
> > tlb_change_page_size(tlb, PAGE_SIZE);
> > orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > flush_tlb_batched_pending(mm);
> > @@ -443,6 +495,7 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
> >
> > arch_enter_lazy_mmu_mode();
> > pte_unmap_unlock(orig_pte, ptl);
> > +next:
> > cond_resched();
> >
> > return 0;
> > @@ -493,70 +546,38 @@ static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> > LIST_HEAD(page_list);
> > struct page *page;
> > int isolated = 0;
> > - unsigned long next;
> >
> > if (fatal_signal_pending(current))
> > return -EINTR;
> >
> > - next = pmd_addr_end(addr, end);
> > if (pmd_trans_huge(*pmd)) {
> > - pmd_t orig_pmd;
> > -
> > - tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
> > ptl = pmd_trans_huge_lock(pmd, vma);
> > if (!ptl)
> > return 0;
> >
> > - orig_pmd = *pmd;
> > - if (is_huge_zero_pmd(orig_pmd))
> > - goto huge_unlock;
> > -
> > - if (unlikely(!pmd_present(orig_pmd))) {
> > - VM_BUG_ON(thp_migration_supported() &&
> > - !is_pmd_migration_entry(orig_pmd));
> > - goto huge_unlock;
> > - }
> > -
> > - page = pmd_page(orig_pmd);
> > - if (next - addr != HPAGE_PMD_SIZE) {
> > - int err;
> > -
> > - if (page_mapcount(page) != 1)
> > - goto huge_unlock;
> > - get_page(page);
> > + switch (madvise_pmdp_reset_or_split(walk, pmd, ptl, addr, end,
> > + true, false)) {
> > + case MADV_PMDP_RESET:
> > + page = pmd_page(*pmd);
> > spin_unlock(ptl);
> > - lock_page(page);
> > - err = split_huge_page(page);
> > - unlock_page(page);
> > - put_page(page);
> > - if (!err)
> > - goto regular_page;
> > - return 0;
> > - }
> > -
> > - if (isolate_lru_page(page))
> > - goto huge_unlock;
> > -
> > - if (pmd_young(orig_pmd)) {
> > - pmdp_invalidate(vma, addr, pmd);
> > - orig_pmd = pmd_mkold(orig_pmd);
> > -
> > - set_pmd_at(mm, addr, pmd, orig_pmd);
> > - tlb_remove_tlb_entry(tlb, pmd, addr);
> > + if (isolate_lru_page(page))
> > + return 0;
> > + ClearPageReferenced(page);
> > + test_and_clear_page_young(page);
> > + list_add(&page->lru, &page_list);
> > + reclaim_pages(&page_list);
> > + goto next;
> > + case MADV_PMDP_ERROR:
> > + spin_unlock(ptl);
> > + goto next;
> > + case MADV_PMDP_SPLIT:
> > + ; /* go through */
> > }
> > -
> > - ClearPageReferenced(page);
> > - test_and_clear_page_young(page);
> > - list_add(&page->lru, &page_list);
> > -huge_unlock:
> > - spin_unlock(ptl);
> > - reclaim_pages(&page_list);
> > - return 0;
> > }
> >
> > if (pmd_trans_unstable(pmd))
> > return 0;
> > -regular_page:
> > +
> > tlb_change_page_size(tlb, PAGE_SIZE);
> > orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > flush_tlb_batched_pending(mm);
> > @@ -631,6 +652,7 @@ static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> > arch_leave_lazy_mmu_mode();
> > pte_unmap_unlock(orig_pte, ptl);
> > reclaim_pages(&page_list);
> > +next:
> > cond_resched();
> >
> > return 0;
> > @@ -700,12 +722,26 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> > pte_t *orig_pte, *pte, ptent;
> > struct page *page;
> > int nr_swap = 0;
> > - unsigned long next;
> >
> > - next = pmd_addr_end(addr, end);
> > - if (pmd_trans_huge(*pmd))
> > - if (madvise_free_huge_pmd(tlb, vma, pmd, addr, next))
> > + if (pmd_trans_huge(*pmd)) {
> > + ptl = pmd_trans_huge_lock(pmd, vma);
> > + if (!ptl)
> > + return 0;
> > +
> > + switch (madvise_pmdp_reset_or_split(walk, pmd, ptl, addr, end,
> > + true, true)) {
> > + case MADV_PMDP_RESET:
> > + page = pmd_page(*pmd);
> > + spin_unlock(ptl);
> > + mark_page_lazyfree(page);
> > goto next;
> > + case MADV_PMDP_ERROR:
> > + spin_unlock(ptl);
> > + goto next;
> > + case MADV_PMDP_SPLIT:
> > + ; /* go through */
> > + }
> > + }
> >
> > if (pmd_trans_unstable(pmd))
> > return 0;
> > @@ -817,8 +853,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> > }
> > arch_leave_lazy_mmu_mode();
> > pte_unmap_unlock(orig_pte, ptl);
> > - cond_resched();
> > next:
> > + cond_resched();
> > return 0;
> > }
> >
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
>
> --
> Michal Hocko
> SUSE Labs
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