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Message-ID: <20190709141019.GN26380@dhcp22.suse.cz>
Date: Tue, 9 Jul 2019 16:10:19 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Minchan Kim <minchan@...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 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.
> 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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