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Date: Wed, 9 Mar 2022 16:26:33 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Muchun Song <songmuchun@...edance.com>
Cc: Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Alistair Popple <apopple@...dia.com>,
Yang Shi <shy828301@...il.com>,
Ralph Campbell <rcampbell@...dia.com>,
Hugh Dickins <hughd@...gle.com>, xiyuyang19@...an.edu.cn,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Ross Zwisler <zwisler@...nel.org>,
Christoph Hellwig <hch@...radead.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
Linux NVDIMM <nvdimm@...ts.linux.dev>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux MM <linux-mm@...ck.org>, duanxiongchun@...edance.com,
Muchun Song <smuchun@...il.com>
Subject: Re: [PATCH v4 3/6] mm: rmap: introduce pfn_mkclean_range() to cleans PTEs
On Wed, Mar 2, 2022 at 12:29 AM Muchun Song <songmuchun@...edance.com> wrote:
>
> The page_mkclean_one() is supposed to be used with the pfn that has a
> associated struct page, but not all the pfns (e.g. DAX) have a struct
> page. Introduce a new function pfn_mkclean_range() to cleans the PTEs
> (including PMDs) mapped with range of pfns which has no struct page
> associated with them. This helper will be used by DAX device in the
> next patch to make pfns clean.
This seems unfortunate given the desire to kill off
CONFIG_FS_DAX_LIMITED which is the only way to get DAX without 'struct
page'.
I would special case these helpers behind CONFIG_FS_DAX_LIMITED such
that they can be deleted when that support is finally removed.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
> include/linux/rmap.h | 3 +++
> mm/internal.h | 26 +++++++++++++--------
> mm/rmap.c | 65 +++++++++++++++++++++++++++++++++++++++++++---------
> 3 files changed, 74 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index b58ddb8b2220..a6ec0d3e40c1 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -263,6 +263,9 @@ unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
> */
> int folio_mkclean(struct folio *);
>
> +int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
> + struct vm_area_struct *vma);
> +
> void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked);
>
> /*
> diff --git a/mm/internal.h b/mm/internal.h
> index f45292dc4ef5..ff873944749f 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -516,26 +516,22 @@ void mlock_page_drain(int cpu);
> extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
>
> /*
> - * At what user virtual address is page expected in vma?
> - * Returns -EFAULT if all of the page is outside the range of vma.
> - * If page is a compound head, the entire compound page is considered.
> + * * Return the start of user virtual address at the specific offset within
> + * a vma.
> */
> static inline unsigned long
> -vma_address(struct page *page, struct vm_area_struct *vma)
> +vma_pgoff_address(pgoff_t pgoff, unsigned long nr_pages,
> + struct vm_area_struct *vma)
> {
> - pgoff_t pgoff;
> unsigned long address;
>
> - VM_BUG_ON_PAGE(PageKsm(page), page); /* KSM page->index unusable */
> - pgoff = page_to_pgoff(page);
> if (pgoff >= vma->vm_pgoff) {
> address = vma->vm_start +
> ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> /* Check for address beyond vma (or wrapped through 0?) */
> if (address < vma->vm_start || address >= vma->vm_end)
> address = -EFAULT;
> - } else if (PageHead(page) &&
> - pgoff + compound_nr(page) - 1 >= vma->vm_pgoff) {
> + } else if (pgoff + nr_pages - 1 >= vma->vm_pgoff) {
> /* Test above avoids possibility of wrap to 0 on 32-bit */
> address = vma->vm_start;
> } else {
> @@ -545,6 +541,18 @@ vma_address(struct page *page, struct vm_area_struct *vma)
> }
>
> /*
> + * Return the start of user virtual address of a page within a vma.
> + * Returns -EFAULT if all of the page is outside the range of vma.
> + * If page is a compound head, the entire compound page is considered.
> + */
> +static inline unsigned long
> +vma_address(struct page *page, struct vm_area_struct *vma)
> +{
> + VM_BUG_ON_PAGE(PageKsm(page), page); /* KSM page->index unusable */
> + return vma_pgoff_address(page_to_pgoff(page), compound_nr(page), vma);
> +}
> +
> +/*
> * Then at what user virtual address will none of the range be found in vma?
> * Assumes that vma_address() already returned a good starting address.
> */
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 723682ddb9e8..ad5cf0e45a73 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -929,12 +929,12 @@ int folio_referenced(struct folio *folio, int is_locked,
> return pra.referenced;
> }
>
> -static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
> - unsigned long address, void *arg)
> +static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
> {
> - DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_SYNC);
> + int cleaned = 0;
> + struct vm_area_struct *vma = pvmw->vma;
> struct mmu_notifier_range range;
> - int *cleaned = arg;
> + unsigned long address = pvmw->address;
>
> /*
> * We have to assume the worse case ie pmd for invalidation. Note that
> @@ -942,16 +942,16 @@ static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
> */
> mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
> 0, vma, vma->vm_mm, address,
> - vma_address_end(&pvmw));
> + vma_address_end(pvmw));
> mmu_notifier_invalidate_range_start(&range);
>
> - while (page_vma_mapped_walk(&pvmw)) {
> + while (page_vma_mapped_walk(pvmw)) {
> int ret = 0;
>
> - address = pvmw.address;
> - if (pvmw.pte) {
> + address = pvmw->address;
> + if (pvmw->pte) {
> pte_t entry;
> - pte_t *pte = pvmw.pte;
> + pte_t *pte = pvmw->pte;
>
> if (!pte_dirty(*pte) && !pte_write(*pte))
> continue;
> @@ -964,7 +964,7 @@ static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
> ret = 1;
> } else {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - pmd_t *pmd = pvmw.pmd;
> + pmd_t *pmd = pvmw->pmd;
> pmd_t entry;
>
> if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
> @@ -991,11 +991,22 @@ static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
> * See Documentation/vm/mmu_notifier.rst
> */
> if (ret)
> - (*cleaned)++;
> + cleaned++;
> }
>
> mmu_notifier_invalidate_range_end(&range);
>
> + return cleaned;
> +}
> +
> +static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
> + unsigned long address, void *arg)
> +{
> + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_SYNC);
> + int *cleaned = arg;
> +
> + *cleaned += page_vma_mkclean_one(&pvmw);
> +
> return true;
> }
>
> @@ -1033,6 +1044,38 @@ int folio_mkclean(struct folio *folio)
> EXPORT_SYMBOL_GPL(folio_mkclean);
>
> /**
> + * pfn_mkclean_range - Cleans the PTEs (including PMDs) mapped with range of
> + * [@pfn, @pfn + @nr_pages) at the specific offset (@pgoff)
> + * within the @vma of shared mappings. And since clean PTEs
> + * should also be readonly, write protects them too.
> + * @pfn: start pfn.
> + * @nr_pages: number of physically contiguous pages srarting with @pfn.
> + * @pgoff: page offset that the @pfn mapped with.
> + * @vma: vma that @pfn mapped within.
> + *
> + * Returns the number of cleaned PTEs (including PMDs).
> + */
> +int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
> + struct vm_area_struct *vma)
> +{
> + struct page_vma_mapped_walk pvmw = {
> + .pfn = pfn,
> + .nr_pages = nr_pages,
> + .pgoff = pgoff,
> + .vma = vma,
> + .flags = PVMW_SYNC,
> + };
> +
> + if (invalid_mkclean_vma(vma, NULL))
> + return 0;
> +
> + pvmw.address = vma_pgoff_address(pgoff, nr_pages, vma);
> + VM_BUG_ON_VMA(pvmw.address == -EFAULT, vma);
> +
> + return page_vma_mkclean_one(&pvmw);
> +}
> +
> +/**
> * page_move_anon_rmap - move a page to our anon_vma
> * @page: the page to move to our anon_vma
> * @vma: the vma the page belongs to
> --
> 2.11.0
>
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